Conceptele de baza pentru algebra relationala. De asemenea, puteti gasi un film cu cursul explicat in limba romana, la aceasta adresa: https://www.youtube.com/watch?v=ioIQf9XGBKA
Primul curs de Baze de date, pentru cei care sunt interesati sa aiba si slidurile. Filmuletul cu prezentarea il puteti gasi aici: https://youtu.be/hOgGML7N730
2024 State of Marketing Report – by HubspotMarius Sescu
https://www.hubspot.com/state-of-marketing
· Scaling relationships and proving ROI
· Social media is the place for search, sales, and service
· Authentic influencer partnerships fuel brand growth
· The strongest connections happen via call, click, chat, and camera.
· Time saved with AI leads to more creative work
· Seeking: A single source of truth
· TLDR; Get on social, try AI, and align your systems.
· More human marketing, powered by robots
ChatGPT is a revolutionary addition to the world since its introduction in 2022. A big shift in the sector of information gathering and processing happened because of this chatbot. What is the story of ChatGPT? How is the bot responding to prompts and generating contents? Swipe through these slides prepared by Expeed Software, a web development company regarding the development and technical intricacies of ChatGPT!
Product Design Trends in 2024 | Teenage EngineeringsPixeldarts
The realm of product design is a constantly changing environment where technology and style intersect. Every year introduces fresh challenges and exciting trends that mold the future of this captivating art form. In this piece, we delve into the significant trends set to influence the look and functionality of product design in the year 2024.
Primul curs de Baze de date, pentru cei care sunt interesati sa aiba si slidurile. Filmuletul cu prezentarea il puteti gasi aici: https://youtu.be/hOgGML7N730
2024 State of Marketing Report – by HubspotMarius Sescu
https://www.hubspot.com/state-of-marketing
· Scaling relationships and proving ROI
· Social media is the place for search, sales, and service
· Authentic influencer partnerships fuel brand growth
· The strongest connections happen via call, click, chat, and camera.
· Time saved with AI leads to more creative work
· Seeking: A single source of truth
· TLDR; Get on social, try AI, and align your systems.
· More human marketing, powered by robots
ChatGPT is a revolutionary addition to the world since its introduction in 2022. A big shift in the sector of information gathering and processing happened because of this chatbot. What is the story of ChatGPT? How is the bot responding to prompts and generating contents? Swipe through these slides prepared by Expeed Software, a web development company regarding the development and technical intricacies of ChatGPT!
Product Design Trends in 2024 | Teenage EngineeringsPixeldarts
The realm of product design is a constantly changing environment where technology and style intersect. Every year introduces fresh challenges and exciting trends that mold the future of this captivating art form. In this piece, we delve into the significant trends set to influence the look and functionality of product design in the year 2024.
How Race, Age and Gender Shape Attitudes Towards Mental HealthThinkNow
Mental health has been in the news quite a bit lately. Dozens of U.S. states are currently suing Meta for contributing to the youth mental health crisis by inserting addictive features into their products, while the U.S. Surgeon General is touring the nation to bring awareness to the growing epidemic of loneliness and isolation. The country has endured periods of low national morale, such as in the 1970s when high inflation and the energy crisis worsened public sentiment following the Vietnam War. The current mood, however, feels different. Gallup recently reported that national mental health is at an all-time low, with few bright spots to lift spirits.
To better understand how Americans are feeling and their attitudes towards mental health in general, ThinkNow conducted a nationally representative quantitative survey of 1,500 respondents and found some interesting differences among ethnic, age and gender groups.
Technology
For example, 52% agree that technology and social media have a negative impact on mental health, but when broken out by race, 61% of Whites felt technology had a negative effect, and only 48% of Hispanics thought it did.
While technology has helped us keep in touch with friends and family in faraway places, it appears to have degraded our ability to connect in person. Staying connected online is a double-edged sword since the same news feed that brings us pictures of the grandkids and fluffy kittens also feeds us news about the wars in Israel and Ukraine, the dysfunction in Washington, the latest mass shooting and the climate crisis.
Hispanics may have a built-in defense against the isolation technology breeds, owing to their large, multigenerational households, strong social support systems, and tendency to use social media to stay connected with relatives abroad.
Age and Gender
When asked how individuals rate their mental health, men rate it higher than women by 11 percentage points, and Baby Boomers rank it highest at 83%, saying it’s good or excellent vs. 57% of Gen Z saying the same.
Gen Z spends the most amount of time on social media, so the notion that social media negatively affects mental health appears to be correlated. Unfortunately, Gen Z is also the generation that’s least comfortable discussing mental health concerns with healthcare professionals. Only 40% of them state they’re comfortable discussing their issues with a professional compared to 60% of Millennials and 65% of Boomers.
Race Affects Attitudes
As seen in previous research conducted by ThinkNow, Asian Americans lag other groups when it comes to awareness of mental health issues. Twenty-four percent of Asian Americans believe that having a mental health issue is a sign of weakness compared to the 16% average for all groups. Asians are also considerably less likely to be aware of mental health services in their communities (42% vs. 55%) and most likely to seek out information on social media (51% vs. 35%).
AI Trends in Creative Operations 2024 by Artwork Flow.pdfmarketingartwork
Creative operations teams expect increased AI use in 2024. Currently, over half of tasks are not AI-enabled, but this is expected to decrease in the coming year. ChatGPT is the most popular AI tool currently. Business leaders are more actively exploring AI benefits than individual contributors. Most respondents do not believe AI will impact workforce size in 2024. However, some inhibitions still exist around AI accuracy and lack of understanding. Creatives primarily want to use AI to save time on mundane tasks and boost productivity.
Organizational culture includes values, norms, systems, symbols, language, assumptions, beliefs, and habits that influence employee behaviors and how people interpret those behaviors. It is important because culture can help or hinder a company's success. Some key aspects of Netflix's culture that help it achieve results include hiring smartly so every position has stars, focusing on attitude over just aptitude, and having a strict policy against peacocks, whiners, and jerks.
PEPSICO Presentation to CAGNY Conference Feb 2024Neil Kimberley
PepsiCo provided a safe harbor statement noting that any forward-looking statements are based on currently available information and are subject to risks and uncertainties. It also provided information on non-GAAP measures and directing readers to its website for disclosure and reconciliation. The document then discussed PepsiCo's business overview, including that it is a global beverage and convenient food company with iconic brands, $91 billion in net revenue in 2023, and nearly $14 billion in core operating profit. It operates through a divisional structure with a focus on local consumers.
Content Methodology: A Best Practices Report (Webinar)contently
This document provides an overview of content methodology best practices. It defines content methodology as establishing objectives, KPIs, and a culture of continuous learning and iteration. An effective methodology focuses on connecting with audiences, creating optimal content, and optimizing processes. It also discusses why a methodology is needed due to the competitive landscape, proliferation of channels, and opportunities for improvement. Components of an effective methodology include defining objectives and KPIs, audience analysis, identifying opportunities, and evaluating resources. The document concludes with recommendations around creating a content plan, testing and optimizing content over 90 days.
How to Prepare For a Successful Job Search for 2024Albert Qian
The document provides guidance on preparing a job search for 2024. It discusses the state of the job market, focusing on growth in AI and healthcare but also continued layoffs. It recommends figuring out what you want to do by researching interests and skills, then conducting informational interviews. The job search should involve building a personal brand on LinkedIn, actively applying to jobs, tailoring resumes and interviews, maintaining job hunting as a habit, and continuing self-improvement. Once hired, the document advises setting new goals and keeping skills and networking active in case of future opportunities.
A report by thenetworkone and Kurio.
The contributing experts and agencies are (in an alphabetical order): Sylwia Rytel, Social Media Supervisor, 180heartbeats + JUNG v MATT (PL), Sharlene Jenner, Vice President - Director of Engagement Strategy, Abelson Taylor (USA), Alex Casanovas, Digital Director, Atrevia (ES), Dora Beilin, Senior Social Strategist, Barrett Hoffher (USA), Min Seo, Campaign Director, Brand New Agency (KR), Deshé M. Gully, Associate Strategist, Day One Agency (USA), Francesca Trevisan, Strategist, Different (IT), Trevor Crossman, CX and Digital Transformation Director; Olivia Hussey, Strategic Planner; Simi Srinarula, Social Media Manager, The Hallway (AUS), James Hebbert, Managing Director, Hylink (CN / UK), Mundy Álvarez, Planning Director; Pedro Rojas, Social Media Manager; Pancho González, CCO, Inbrax (CH), Oana Oprea, Head of Digital Planning, Jam Session Agency (RO), Amy Bottrill, Social Account Director, Launch (UK), Gaby Arriaga, Founder, Leonardo1452 (MX), Shantesh S Row, Creative Director, Liwa (UAE), Rajesh Mehta, Chief Strategy Officer; Dhruv Gaur, Digital Planning Lead; Leonie Mergulhao, Account Supervisor - Social Media & PR, Medulla (IN), Aurelija Plioplytė, Head of Digital & Social, Not Perfect (LI), Daiana Khaidargaliyeva, Account Manager, Osaka Labs (UK / USA), Stefanie Söhnchen, Vice President Digital, PIABO Communications (DE), Elisabeth Winiartati, Managing Consultant, Head of Global Integrated Communications; Lydia Aprina, Account Manager, Integrated Marketing and Communications; Nita Prabowo, Account Manager, Integrated Marketing and Communications; Okhi, Web Developer, PNTR Group (ID), Kei Obusan, Insights Director; Daffi Ranandi, Insights Manager, Radarr (SG), Gautam Reghunath, Co-founder & CEO, Talented (IN), Donagh Humphreys, Head of Social and Digital Innovation, THINKHOUSE (IRE), Sarah Yim, Strategy Director, Zulu Alpha Kilo (CA).
Trends In Paid Search: Navigating The Digital Landscape In 2024Search Engine Journal
The search marketing landscape is evolving rapidly with new technologies, and professionals, like you, rely on innovative paid search strategies to meet changing demands.
It’s important that you’re ready to implement new strategies in 2024.
Check this out and learn the top trends in paid search advertising that are expected to gain traction, so you can drive higher ROI more efficiently in 2024.
You’ll learn:
- The latest trends in AI and automation, and what this means for an evolving paid search ecosystem.
- New developments in privacy and data regulation.
- Emerging ad formats that are expected to make an impact next year.
Watch Sreekant Lanka from iQuanti and Irina Klein from OneMain Financial as they dive into the future of paid search and explore the trends, strategies, and technologies that will shape the search marketing landscape.
If you’re looking to assess your paid search strategy and design an industry-aligned plan for 2024, then this webinar is for you.
5 Public speaking tips from TED - Visualized summarySpeakerHub
From their humble beginnings in 1984, TED has grown into the world’s most powerful amplifier for speakers and thought-leaders to share their ideas. They have over 2,400 filmed talks (not including the 30,000+ TEDx videos) freely available online, and have hosted over 17,500 events around the world.
With over one billion views in a year, it’s no wonder that so many speakers are looking to TED for ideas on how to share their message more effectively.
The article “5 Public-Speaking Tips TED Gives Its Speakers”, by Carmine Gallo for Forbes, gives speakers five practical ways to connect with their audience, and effectively share their ideas on stage.
Whether you are gearing up to get on a TED stage yourself, or just want to master the skills that so many of their speakers possess, these tips and quotes from Chris Anderson, the TED Talks Curator, will encourage you to make the most impactful impression on your audience.
See the full article and more summaries like this on SpeakerHub here: https://speakerhub.com/blog/5-presentation-tips-ted-gives-its-speakers
See the original article on Forbes here:
http://www.forbes.com/forbes/welcome/?toURL=http://www.forbes.com/sites/carminegallo/2016/05/06/5-public-speaking-tips-ted-gives-its-speakers/&refURL=&referrer=#5c07a8221d9b
ChatGPT and the Future of Work - Clark Boyd Clark Boyd
Everyone is in agreement that ChatGPT (and other generative AI tools) will shape the future of work. Yet there is little consensus on exactly how, when, and to what extent this technology will change our world.
Businesses that extract maximum value from ChatGPT will use it as a collaborative tool for everything from brainstorming to technical maintenance.
For individuals, now is the time to pinpoint the skills the future professional will need to thrive in the AI age.
Check out this presentation to understand what ChatGPT is, how it will shape the future of work, and how you can prepare to take advantage.
The document provides career advice for getting into the tech field, including:
- Doing projects and internships in college to build a portfolio.
- Learning about different roles and technologies through industry research.
- Contributing to open source projects to build experience and network.
- Developing a personal brand through a website and social media presence.
- Networking through events, communities, and finding a mentor.
- Practicing interviews through mock interviews and whiteboarding coding questions.
Google's Just Not That Into You: Understanding Core Updates & Search IntentLily Ray
1. Core updates from Google periodically change how its algorithms assess and rank websites and pages. This can impact rankings through shifts in user intent, site quality issues being caught up to, world events influencing queries, and overhauls to search like the E-A-T framework.
2. There are many possible user intents beyond just transactional, navigational and informational. Identifying intent shifts is important during core updates. Sites may need to optimize for new intents through different content types and sections.
3. Responding effectively to core updates requires analyzing "before and after" data to understand changes, identifying new intents or page types, and ensuring content matches appropriate intents across video, images, knowledge graphs and more.
A brief introduction to DataScience with explaining of the concepts, algorithms, machine learning, supervised and unsupervised learning, clustering, statistics, data preprocessing, real-world applications etc.
It's part of a Data Science Corner Campaign where I will be discussing the fundamentals of DataScience, AIML, Statistics etc.
Time Management & Productivity - Best PracticesVit Horky
Here's my presentation on by proven best practices how to manage your work time effectively and how to improve your productivity. It includes practical tips and how to use tools such as Slack, Google Apps, Hubspot, Google Calendar, Gmail and others.
The six step guide to practical project managementMindGenius
The six step guide to practical project management
If you think managing projects is too difficult, think again.
We’ve stripped back project management processes to the
basics – to make it quicker and easier, without sacrificing
the vital ingredients for success.
“If you’re looking for some real-world guidance, then The Six Step Guide to Practical Project Management will help.”
Dr Andrew Makar, Tactical Project Management
Unlocking the Power of ChatGPT and AI in Testing - A Real-World Look, present...Applitools
During this webinar, Anand Bagmar demonstrates how AI tools such as ChatGPT can be applied to various stages of the software development life cycle (SDLC) using an eCommerce application case study. Find the on-demand recording and more info at https://applitools.info/b59
Key takeaways:
• Learn how to use ChatGPT to add AI power to your testing and test automation
• Understand the limitations of the technology and where human expertise is crucial
• Gain insight into different AI-based tools
• Adopt AI-based tools to stay relevant and optimize work for developers and testers
* ChatGPT and OpenAI belong to OpenAI, L.L.C.
The document discusses various AI tools from OpenAI like GPT-3 and DALL-E 2, as well as ChatGPT. It explores how search engines are using AI and things to consider around AI-generated content. Potential SEO uses of ChatGPT are also presented, such as generating content at scale, conducting topic research, and automating basic coding tasks. The document encourages further reading on using ChatGPT for SEO purposes.
How Race, Age and Gender Shape Attitudes Towards Mental HealthThinkNow
Mental health has been in the news quite a bit lately. Dozens of U.S. states are currently suing Meta for contributing to the youth mental health crisis by inserting addictive features into their products, while the U.S. Surgeon General is touring the nation to bring awareness to the growing epidemic of loneliness and isolation. The country has endured periods of low national morale, such as in the 1970s when high inflation and the energy crisis worsened public sentiment following the Vietnam War. The current mood, however, feels different. Gallup recently reported that national mental health is at an all-time low, with few bright spots to lift spirits.
To better understand how Americans are feeling and their attitudes towards mental health in general, ThinkNow conducted a nationally representative quantitative survey of 1,500 respondents and found some interesting differences among ethnic, age and gender groups.
Technology
For example, 52% agree that technology and social media have a negative impact on mental health, but when broken out by race, 61% of Whites felt technology had a negative effect, and only 48% of Hispanics thought it did.
While technology has helped us keep in touch with friends and family in faraway places, it appears to have degraded our ability to connect in person. Staying connected online is a double-edged sword since the same news feed that brings us pictures of the grandkids and fluffy kittens also feeds us news about the wars in Israel and Ukraine, the dysfunction in Washington, the latest mass shooting and the climate crisis.
Hispanics may have a built-in defense against the isolation technology breeds, owing to their large, multigenerational households, strong social support systems, and tendency to use social media to stay connected with relatives abroad.
Age and Gender
When asked how individuals rate their mental health, men rate it higher than women by 11 percentage points, and Baby Boomers rank it highest at 83%, saying it’s good or excellent vs. 57% of Gen Z saying the same.
Gen Z spends the most amount of time on social media, so the notion that social media negatively affects mental health appears to be correlated. Unfortunately, Gen Z is also the generation that’s least comfortable discussing mental health concerns with healthcare professionals. Only 40% of them state they’re comfortable discussing their issues with a professional compared to 60% of Millennials and 65% of Boomers.
Race Affects Attitudes
As seen in previous research conducted by ThinkNow, Asian Americans lag other groups when it comes to awareness of mental health issues. Twenty-four percent of Asian Americans believe that having a mental health issue is a sign of weakness compared to the 16% average for all groups. Asians are also considerably less likely to be aware of mental health services in their communities (42% vs. 55%) and most likely to seek out information on social media (51% vs. 35%).
AI Trends in Creative Operations 2024 by Artwork Flow.pdfmarketingartwork
Creative operations teams expect increased AI use in 2024. Currently, over half of tasks are not AI-enabled, but this is expected to decrease in the coming year. ChatGPT is the most popular AI tool currently. Business leaders are more actively exploring AI benefits than individual contributors. Most respondents do not believe AI will impact workforce size in 2024. However, some inhibitions still exist around AI accuracy and lack of understanding. Creatives primarily want to use AI to save time on mundane tasks and boost productivity.
Organizational culture includes values, norms, systems, symbols, language, assumptions, beliefs, and habits that influence employee behaviors and how people interpret those behaviors. It is important because culture can help or hinder a company's success. Some key aspects of Netflix's culture that help it achieve results include hiring smartly so every position has stars, focusing on attitude over just aptitude, and having a strict policy against peacocks, whiners, and jerks.
PEPSICO Presentation to CAGNY Conference Feb 2024Neil Kimberley
PepsiCo provided a safe harbor statement noting that any forward-looking statements are based on currently available information and are subject to risks and uncertainties. It also provided information on non-GAAP measures and directing readers to its website for disclosure and reconciliation. The document then discussed PepsiCo's business overview, including that it is a global beverage and convenient food company with iconic brands, $91 billion in net revenue in 2023, and nearly $14 billion in core operating profit. It operates through a divisional structure with a focus on local consumers.
Content Methodology: A Best Practices Report (Webinar)contently
This document provides an overview of content methodology best practices. It defines content methodology as establishing objectives, KPIs, and a culture of continuous learning and iteration. An effective methodology focuses on connecting with audiences, creating optimal content, and optimizing processes. It also discusses why a methodology is needed due to the competitive landscape, proliferation of channels, and opportunities for improvement. Components of an effective methodology include defining objectives and KPIs, audience analysis, identifying opportunities, and evaluating resources. The document concludes with recommendations around creating a content plan, testing and optimizing content over 90 days.
How to Prepare For a Successful Job Search for 2024Albert Qian
The document provides guidance on preparing a job search for 2024. It discusses the state of the job market, focusing on growth in AI and healthcare but also continued layoffs. It recommends figuring out what you want to do by researching interests and skills, then conducting informational interviews. The job search should involve building a personal brand on LinkedIn, actively applying to jobs, tailoring resumes and interviews, maintaining job hunting as a habit, and continuing self-improvement. Once hired, the document advises setting new goals and keeping skills and networking active in case of future opportunities.
A report by thenetworkone and Kurio.
The contributing experts and agencies are (in an alphabetical order): Sylwia Rytel, Social Media Supervisor, 180heartbeats + JUNG v MATT (PL), Sharlene Jenner, Vice President - Director of Engagement Strategy, Abelson Taylor (USA), Alex Casanovas, Digital Director, Atrevia (ES), Dora Beilin, Senior Social Strategist, Barrett Hoffher (USA), Min Seo, Campaign Director, Brand New Agency (KR), Deshé M. Gully, Associate Strategist, Day One Agency (USA), Francesca Trevisan, Strategist, Different (IT), Trevor Crossman, CX and Digital Transformation Director; Olivia Hussey, Strategic Planner; Simi Srinarula, Social Media Manager, The Hallway (AUS), James Hebbert, Managing Director, Hylink (CN / UK), Mundy Álvarez, Planning Director; Pedro Rojas, Social Media Manager; Pancho González, CCO, Inbrax (CH), Oana Oprea, Head of Digital Planning, Jam Session Agency (RO), Amy Bottrill, Social Account Director, Launch (UK), Gaby Arriaga, Founder, Leonardo1452 (MX), Shantesh S Row, Creative Director, Liwa (UAE), Rajesh Mehta, Chief Strategy Officer; Dhruv Gaur, Digital Planning Lead; Leonie Mergulhao, Account Supervisor - Social Media & PR, Medulla (IN), Aurelija Plioplytė, Head of Digital & Social, Not Perfect (LI), Daiana Khaidargaliyeva, Account Manager, Osaka Labs (UK / USA), Stefanie Söhnchen, Vice President Digital, PIABO Communications (DE), Elisabeth Winiartati, Managing Consultant, Head of Global Integrated Communications; Lydia Aprina, Account Manager, Integrated Marketing and Communications; Nita Prabowo, Account Manager, Integrated Marketing and Communications; Okhi, Web Developer, PNTR Group (ID), Kei Obusan, Insights Director; Daffi Ranandi, Insights Manager, Radarr (SG), Gautam Reghunath, Co-founder & CEO, Talented (IN), Donagh Humphreys, Head of Social and Digital Innovation, THINKHOUSE (IRE), Sarah Yim, Strategy Director, Zulu Alpha Kilo (CA).
Trends In Paid Search: Navigating The Digital Landscape In 2024Search Engine Journal
The search marketing landscape is evolving rapidly with new technologies, and professionals, like you, rely on innovative paid search strategies to meet changing demands.
It’s important that you’re ready to implement new strategies in 2024.
Check this out and learn the top trends in paid search advertising that are expected to gain traction, so you can drive higher ROI more efficiently in 2024.
You’ll learn:
- The latest trends in AI and automation, and what this means for an evolving paid search ecosystem.
- New developments in privacy and data regulation.
- Emerging ad formats that are expected to make an impact next year.
Watch Sreekant Lanka from iQuanti and Irina Klein from OneMain Financial as they dive into the future of paid search and explore the trends, strategies, and technologies that will shape the search marketing landscape.
If you’re looking to assess your paid search strategy and design an industry-aligned plan for 2024, then this webinar is for you.
5 Public speaking tips from TED - Visualized summarySpeakerHub
From their humble beginnings in 1984, TED has grown into the world’s most powerful amplifier for speakers and thought-leaders to share their ideas. They have over 2,400 filmed talks (not including the 30,000+ TEDx videos) freely available online, and have hosted over 17,500 events around the world.
With over one billion views in a year, it’s no wonder that so many speakers are looking to TED for ideas on how to share their message more effectively.
The article “5 Public-Speaking Tips TED Gives Its Speakers”, by Carmine Gallo for Forbes, gives speakers five practical ways to connect with their audience, and effectively share their ideas on stage.
Whether you are gearing up to get on a TED stage yourself, or just want to master the skills that so many of their speakers possess, these tips and quotes from Chris Anderson, the TED Talks Curator, will encourage you to make the most impactful impression on your audience.
See the full article and more summaries like this on SpeakerHub here: https://speakerhub.com/blog/5-presentation-tips-ted-gives-its-speakers
See the original article on Forbes here:
http://www.forbes.com/forbes/welcome/?toURL=http://www.forbes.com/sites/carminegallo/2016/05/06/5-public-speaking-tips-ted-gives-its-speakers/&refURL=&referrer=#5c07a8221d9b
ChatGPT and the Future of Work - Clark Boyd Clark Boyd
Everyone is in agreement that ChatGPT (and other generative AI tools) will shape the future of work. Yet there is little consensus on exactly how, when, and to what extent this technology will change our world.
Businesses that extract maximum value from ChatGPT will use it as a collaborative tool for everything from brainstorming to technical maintenance.
For individuals, now is the time to pinpoint the skills the future professional will need to thrive in the AI age.
Check out this presentation to understand what ChatGPT is, how it will shape the future of work, and how you can prepare to take advantage.
The document provides career advice for getting into the tech field, including:
- Doing projects and internships in college to build a portfolio.
- Learning about different roles and technologies through industry research.
- Contributing to open source projects to build experience and network.
- Developing a personal brand through a website and social media presence.
- Networking through events, communities, and finding a mentor.
- Practicing interviews through mock interviews and whiteboarding coding questions.
Google's Just Not That Into You: Understanding Core Updates & Search IntentLily Ray
1. Core updates from Google periodically change how its algorithms assess and rank websites and pages. This can impact rankings through shifts in user intent, site quality issues being caught up to, world events influencing queries, and overhauls to search like the E-A-T framework.
2. There are many possible user intents beyond just transactional, navigational and informational. Identifying intent shifts is important during core updates. Sites may need to optimize for new intents through different content types and sections.
3. Responding effectively to core updates requires analyzing "before and after" data to understand changes, identifying new intents or page types, and ensuring content matches appropriate intents across video, images, knowledge graphs and more.
A brief introduction to DataScience with explaining of the concepts, algorithms, machine learning, supervised and unsupervised learning, clustering, statistics, data preprocessing, real-world applications etc.
It's part of a Data Science Corner Campaign where I will be discussing the fundamentals of DataScience, AIML, Statistics etc.
Time Management & Productivity - Best PracticesVit Horky
Here's my presentation on by proven best practices how to manage your work time effectively and how to improve your productivity. It includes practical tips and how to use tools such as Slack, Google Apps, Hubspot, Google Calendar, Gmail and others.
The six step guide to practical project managementMindGenius
The six step guide to practical project management
If you think managing projects is too difficult, think again.
We’ve stripped back project management processes to the
basics – to make it quicker and easier, without sacrificing
the vital ingredients for success.
“If you’re looking for some real-world guidance, then The Six Step Guide to Practical Project Management will help.”
Dr Andrew Makar, Tactical Project Management
Unlocking the Power of ChatGPT and AI in Testing - A Real-World Look, present...Applitools
During this webinar, Anand Bagmar demonstrates how AI tools such as ChatGPT can be applied to various stages of the software development life cycle (SDLC) using an eCommerce application case study. Find the on-demand recording and more info at https://applitools.info/b59
Key takeaways:
• Learn how to use ChatGPT to add AI power to your testing and test automation
• Understand the limitations of the technology and where human expertise is crucial
• Gain insight into different AI-based tools
• Adopt AI-based tools to stay relevant and optimize work for developers and testers
* ChatGPT and OpenAI belong to OpenAI, L.L.C.
The document discusses various AI tools from OpenAI like GPT-3 and DALL-E 2, as well as ChatGPT. It explores how search engines are using AI and things to consider around AI-generated content. Potential SEO uses of ChatGPT are also presented, such as generating content at scale, conducting topic research, and automating basic coding tasks. The document encourages further reading on using ChatGPT for SEO purposes.
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Baze de date - Algebra relat¸ional˘a
Baze de date
Algebra relat¸ional˘a
Nicolae-Cosmin Vˆarlan
October 17, 2018
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Elemente ale modelului relat¸ional
U mult¸ime de atribute: U = {A1, A2, . . . , An};
dom(Ai) - domeniul valorilor atributului Ai;
Definim uplu peste U ca fiind funct¸ia:
ϕ : U →
1≤i≤n
dom(Ai) a.i. ϕ(Ai) ∈ dom(Ai), 1 ≤ i ≤ n
Fie valorile vi astfel ˆıncˆat vi = ϕ(Ai).
Not˘am cu {A1 : v1, A2 : v2, . . . , An : vn} asocierea dintre
atributele existente ˆın U ¸si valorile acestora. ˆIn cazul ˆın care sunt
considerate mult¸imi ordonate (de forma (A1, A2, . . . , An)), notat¸ia
va fi de forma: (v1, v2, . . . , vn).
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
3. 3/ 37
Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Elemente ale modelului relat¸ional
Consider˘am mult¸imea ordonat˘a (A1, A2, . . . An). Pentru orice uplu
ϕ, exist˘a vectorul (v1, v2, . . . vn) a.ˆı. ϕ(Ai) = vi, 1 ≤ i ≤ n.
Pentru un vector (v1, v2, . . . vn) cu vi ∈ dom(Ai), 1 ≤ i ≤ n exist˘a
un uplu ϕ a.ˆı. ϕ(Ai) = vi.
ˆIn practic˘a este considerat˘a o anumit˘a ordonare a atributelor.
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Elemente ale modelului relat¸ional
O mult¸ime de uple peste U se nume¸ste relat¸ie ¸si se noteaz˘a cu r.
r poate varia ˆın timp dar nu ¸si ˆın structur˘a.
Exemplu:
r = {(v11, v12, . . . v1n), (v21, v22, . . . v2n), . . . , (vm1, vm2, . . . vmn)}.
Structura relat¸iei se va nota cu R[U] unde R se nume¸ste numele
relat¸iei iar U este mult¸imea de atribute corespunz˘atoare.
Notat¸ii echivalente R(U), R(A1, A2, . . . , An), R[A1, A2, . . . , An].
R[U] se mai nume¸ste ¸si schem˘a de relat¸ie.
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Elemente ale modelului relat¸ional
ˆIn practic˘a, o relat¸ie r poate fi reprezentat˘a printr-o matrice:
r :
A1 A2 . . . An
v11 v12 . . . v1n
. . . . . . . . . . . .
vm1 vm2 . . . vmn
unde (vi1, vi2, . . . , vin) este un uplu din r, 1 ≤ i ≤ m ¸si
vij ∈ dom(Aj), 1 ≤ j ≤ n, 1 ≤ i ≤ m
Vom nota cu ti linia (tuplul) cu num˘arul i din matrice:
ti = (vi1, vi2, . . . , vin), ∀i ∈ [1, m]
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Elemente ale modelului relat¸ional
O mult¸ime finit˘a D de scheme de relat¸ie se nume¸ste schem˘a de
baze de date. Formal, D = {R1[U1], . . . , Rh[Uh]} unde Ri[Ui] este
o schem˘a de relat¸ie, 1 ≤ i ≤ h.
O baz˘a de date peste D este o corespondent¸˘a ce asociaz˘a fiec˘arei
scheme de relat¸ie din D o relat¸ie.
Exemplu:
r1, r2, . . . rh este o baz˘a de date peste D = {R1[U1], . . . , Rh[Uh]}.
Considerˆand D ca fiind ordonat˘a D = (R1[U1], . . . , Rh[Uh]),
putem nota baza de date sub forma (r1, r2, . . . rh)
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Corespondent¸a cu terminologia din practic˘a
atribut (Ai) = denumirea unei coloane dintr-un tabel;
valoarea atributului Ai (ϕ(Ai) sau vi) = valoarea dintr-o
celul˘a a tabelului
relat¸ie (r) = tabel
schema de relat¸ie (R[U]) = schema tabelei
tuplu (ti) = linie din tabel
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
8. 8/ 37
Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii
Asupra unei mult¸imi de relat¸ii putem efectua o serie de operat¸ii.
Exist˘a dou˘a categorii de operatori:
Operatori din teoria mult¸imilor: Reuniunea(∪), Intersect¸ia
(∩), Diferent¸a(−), Produsul Cartezian(×)
Operatori specifici algebrei relat¸ionale: Proiect¸ia (π),
Select¸ia(σ), Redenumirea(ρ), Joinul Natural( ), θ-Joinul,
equijoinul, Semijoinul( ¸si ), Antijoinul( ), Divizarea(÷),
Joinul la Stˆanga ( ), Joinul la Dreapta( ), Joinul
Exterior( )
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii pe mult¸imi de tuple - Reuniunea: ∪
ˆIn cazul operat¸iilor pe mult¸imi (cu except¸ia Produsului Cartezian),
acestea se realizeaz˘a ˆıntre dou˘a relat¸ii r1 ¸si r2 care sunt
NEAP˘ARAT construite peste aceea¸si mult¸ime de atribute.
Reuniunea a dou˘a relat¸ii r1 ¸si r2, ambele peste o aceea¸si mult¸ime
de atribute U (sau peste aceea¸si schem˘a de relat¸ie R[U]), este o
relat¸ie notat˘a cu r1 ∪ r2 definit˘a astfel:
r1 ∪ r2 = {t | t = uplu, t ∈ r1 sau t ∈ r2}
ˆIn practic˘a, acest lucru se realizeaz˘a utilizˆand cuvˆantul cheie
UNION. Student¸ii din anii 1 ¸si 3 sunt selectat¸i de interogarea:
SELECT * FROM studenti WHERE an=1
UNION
SELECT * FROM studenti WHERE an=3;
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii pe mult¸imi de tuple - Diferent¸a: −
Diferent¸a a dou˘a relat¸ii r1 ¸si r2, ambele peste o aceea¸si mult¸ime de
atribute U (sau peste aceea¸si schem˘a de relat¸ie R[U]), este o
relat¸ie notat˘a cu r1 − r2 definit˘a astfel:
r1 − r2 = {t | t = uplu, t ∈ r1 si t ∈ r2}
ˆIn practic˘a, acest lucru se realizeaz˘a utilizˆand cuvˆantul cheie
MINUS. Pentru a-i selecta pe student¸ii din anul 2 f˘ar˘a burs˘a,
putem s˘a ˆıi select˘am pe tot¸i student¸ii din anul 2 ¸si apoi s˘a ˆıi
elimin˘am pe cei cu bursa:
SELECT * FROM studenti WHERE an=2
MINUS
SELECT * FROM studenti WHERE bursa IS NOT NULL;
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii pe mult¸imi de tuple - Intersect¸ia: ∩
Intersect¸ia a dou˘a relat¸ii r1 ¸si r2, ambele peste o aceea¸si mult¸ime
de atribute U (sau peste aceea¸si schem˘a de relat¸ie R[U]), este o
relat¸ie notat˘a cu r1 ∩ r2 definit˘a astfel:
r1 ∩ r2 = {t | t = uplu, t ∈ r1 si t ∈ r2}
ˆIn practic˘a, acest lucru se realizeaz˘a utilizˆand cuvˆantul cheie
INTERSECT. Putem afla care student¸i din anul 2 au burs˘a rulˆand:
SELECT * FROM studenti WHERE an=2
INTERSECT
SELECT * FROM studenti WHERE bursa IS NOT NULL;
Operatorul de intersect¸ie poate fi obt¸inut din ceilalt¸i doi:
r1 ∩ r2 = r1 − (r1 − r2).
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii pe mult¸imi de tuple - Produsul Cartezian: ×
Produsul cartezian a dou˘a relat¸ii r1 definit˘a peste R1[U1] ¸si r2
definit˘a peste R2[U2] cu U1 ∩ U2 = ∅ este o relat¸ie notat˘a cu
r1 × r2 definit˘a astfel:
r1 × r2 = {t | t = uplu peste U1 ∪ U2, t[U1] ∈ r1 ¸si t[U2] ∈ r2}
De aceasta dat˘a, cele dou˘a relat¸ii nu trebuie s˘a fie peste aceea¸si
mult¸ime de atribute. Rezultatul va fi o nou˘a relat¸ie peste o
mult¸ime de atribute format˘a din atributele relat¸iilor init¸iale.
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii pe mult¸imi de tuple - Produsul Cartezian: ×
Dac˘a un atribut s-ar repeta, el va fi identificat diferit. Spre
exemplu, chiar dac˘a tabelele note ¸si cursuri au un acela¸si atribut
(id curs), nu se face nici o sincronizare dup˘a acesta ci se vor crea
dou˘a atribute diferite: note.id curs respectiv cursuri.id curs.
Produsul cartezian ˆıntre aceste tabele, ˆın practic˘a, se obt¸ine
executˆand interogarea:
SELECT * FROM cursuri, note;
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii specifice algebrei relat¸ionale
Operat¸iile pe mult¸imi aveau ca elemente tuplele. Uneori aceste
tuple nu sunt compatibile (de exemplu nu putem reuni o relat¸ie
peste R1[U1] cu una peste R2[U2] dac˘a U1 = U2).
Pentru a opera asupra atributelor ce definesc tuplele din rezultat,
avem nevoie de o serie de operatori specifici algebrei relat¸ionale.
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Proiect¸ia: π
Consider˘am:
R[U] = schem˘a de relat¸ie;
X ⊆ U;
t = uplu peste R[U] (t ∈ r).
Se nume¸ste proiect¸ia lui t relativ˘a la X ¸si notat˘a cu πX[t],
restrict¸ia lui t la mult¸imea de atribute X. (Uneori vom scrie t[X])
Exemplu:
Dac˘a U = (A1, A2, . . . , An) atunci t = (v1, v2, . . . , vn).
Consider˘am X = (Ai1 , Ai2 , . . . , Aik
), 1 ≤ i1 < i2 < . . . < ik ≤ n.
atunci πX[t] = (vi1 , vi2 , . . . , vik
);
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Proiect¸ia: π
Dac˘a r este o relat¸ie peste R[U] ¸si X ⊆ U, atunci proiect¸ia lui r
relativ˘a la X este πX[r] = {πX[t] | t ∈ r}
Exemplu:
Dac˘a U = (A1, A2, . . . , An) atunci
r = {(v11, v12, . . . v1n), (v21, v22, . . . v2n), . . . , (vm1, vm2, . . . vmn)}.
Consider˘am X = (Ai1 , Ai2 , . . . , Aik
), 1 ≤ i1 < i2 < . . . < ik ≤ n.
atunci
πX[r] = {(v1i1
, v1i2
, . . . v1ik
), (v2i1
, . . . v2ik
), . . . , (vmi1
, . . . vmik
)}
ˆIn practic˘a, proiect¸ia se realizeaz˘a selectˆand doar anumite cˆampuri
ale tabelei (anumite atribute):
SELECT nume, prenume FROM studenti;
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Proiect¸ia: π
Ca ¸si exemplu, vom scrie o interogare care s˘a returneze toate
persoanele care trec pragul Facult˘at¸ii (student¸i ¸si profesori):
SELECT nume, prenume FROM studenti
UNION
SELECT nume, prenume FROM profesori;
ˆIn cazul ˆın care cele dou˘a cˆampuri (nume, prenume) din cele dou˘a
tabele au acela¸si tip (de exemplu nume este de tip
VARCHAR2(10) ˆın ambele tabele), interogarea va afi¸sa toate
persoanele ce “trec pragul Facult˘at¸ii”.
Observat¸ie: Pentru a modifica tipul nume din tabela profesori la
VARCHAR2(10) executat¸i comanda:
ALTER TABLE profesori MODIFY nume VARCHAR2(10);
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Select¸ia: σ
Fie r o relat¸ie peste R[U], A, B ∈ U ¸si c este o constant˘a
O expresie elementar˘a de select¸ie este definit˘a prin urm˘atoarea
formul˘a (forma Backus-Naur):
e = A ϕ B | A ϕ c | c ϕ B
Unde ϕ este o relat¸ie boolean˘a ˆıntre operanzi.
Se nume¸ste expresie de select¸ie (forma Backus-Naur):
θ = e | θ ∧ θ | θ ∨ θ | (θ)
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Select¸ia: σ
Fie θ o expresie de select¸ie. Atunci:
cˆand θ = A ϕ B, t satisface θ dac˘a are loc πA[t] ϕ πB[t],
cˆand θ = A ϕ c, t satisface θ dac˘a are loc πA[t] ϕ c,
cˆand θ = c ϕ B, t satisface θ dac˘a are loc c ϕ πB[t],
cˆand θ = θ1 ∧ θ2, t satisface θ dac˘a t satisface atˆat pe θ1 cˆat
¸si pe θ2,
cˆand θ = θ1 ∨ θ2, t satisface θ dac˘a t satisface m˘acar pe unul
dintre θ1 ¸si θ2.
Dac˘a θ este o expresie de select¸ie atunci select¸ia se noteaz˘a cu
σθ(r) ¸si este definit˘a ca:
σθ(r) = {t|t ∈ r, t satisface θ}
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
20. 20/ 37
Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Select¸ia: σ
ˆIn SQL, select¸ia se obt¸ine utilizˆand o formul˘a logic˘a ce are rolul de
a selecta doar anumite rˆanduri.
Exemplu:
SELECT * FROM studenti
WHERE ((an=2) AND (bursa IS NULL));
ˆIn acest exemplu, θ1 este an = 2, θ2 este bursa IS NULL,
θ = θ1 ∧ θ2 ¸si r este mult¸imea de rˆanduri din tabela student¸i.
Rezultatul este mult¸imea student¸ilor din anul 2 care nu au burs˘a.
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Redenumirea: ρ
Operatorul de redenumire are rolul de a schimba numele unui
atribut cu alt nume. Formal, dac˘a dorim s˘a schimb˘am atributul A1
ˆın A1 vom utiliza scrierea ρA1/A1
(r). Restul atributelor peste care
a fost construit r vor r˘amˆane neschimbate.
ˆIn SQL, redenumirea se realizeaz˘a prin utilizarea cuvˆantului AS:
Exemplu:
SELECT bursa * 1.25 AS “BursaNoua” FROM studenti;
SELECT bursa + bursa/4 AS “BursaNoua” FROM studenti;
Dac˘a nu am redenumi atributul nou obt¸inut, cele dou˘a relat¸ii ar fi
considerate diferite (ˆın prima numele atributului ar fi “bursa *
1.25”, iar ˆın a doua ar fi fost “bursa + bursa/4”) - ATENTIE cand
introduceti exercitii.
Nicolae-Cosmin Vˆarlan Baze de date Algebra relat¸ional˘a
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Join natural:
Consider˘am:
r1 relat¸ie peste R1[U1];
r2 relat¸ie peste R2[U2];
Se nume¸ste Join natural a relat¸iilor r1 ¸si r2, relat¸ia r1 r2 peste
U1 ∪ U2 definit˘a prin:
r1 r2 = {t | t uplu peste U1 ∪ U2, t[Ui] ∈ ri, i = 1, 2}
Dac˘a R este un nume pentru relat¸ia peste U1 ∪ U2 atunci r1 r2
este definit˘a peste R[U1 ∪ U2]
Pentru simplitate vom nota U1 ∪ U2 cu U1U2.
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Join natural:
Exemplu:
Fie R1[A, B, C, D], si R2[C, D, E] si r1, r2 a.i.:
r1 :
A B C D
0 1 0 0
1 1 0 0
0 0 1 0
1 1 0 1
0 1 0 1
r2 :
C D E
1 1 0
1 1 1
0 0 0
1 0 0
1 0 1
Atunci: r1 r2 :
A B C D E
0 1 0 0 0
1 1 0 0 0
0 0 1 0 0
0 0 1 0 1
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Join natural:
Urm˘atoarea interogare identific˘a cui apart¸ine fiecare nota din
tabelul note. Joinul se face dup˘a cˆampul nr matricol ˆıntre tabelele
studenti ¸si note:
SELECT nume, valoare FROM studenti
NATURAL JOIN note;
SELECT nume, valoare FROM studenti
JOIN note ON studenti.nr matricol = note.nr matricol;
Se poate observa c˘a dac˘a din produsul cartezian am elimina acele
cazuri ˆın care cˆampul “nr matricol” nu este identic ˆın ambele
tabele, am obt¸ine, de fapt, acela¸si rezultat. Din acest motiv, joinul
de mai sus poate fi scris ¸si sub forma:
SELECT nume, valoare FROM studenti,note
WHERE studenti.nr matricol = note.nr matricol;
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Extindere Join natural
Fie ri relat¸ie peste Ri[Ui], i = 1, h atunci:
r1 r2 . . . rh = {t|t uplu peste U1, . . . Uh, a.ˆı. t[Ui] ∈ ri, i = 1, h}
Notat¸ii echivalente:
r1 r2 . . . rh
ri, i = 1, h
∗ ri, i = 1, h
Operat¸ia join este asociativ˘a.
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - θ-join, equijoin
Fie ri peste Ri[Ui], i = 1, 2 cu Aα1 , Aα2 , . . . Aαk
∈ U1 ¸si
Bβ1 , Bβ2 , . . . Bβk
∈ U2 ¸si
θi : dom(Aαi ) × dom(Bβi
) → {true, false}, ∀i = 1, k
θ-joinul a dou˘a relat¸ii r1 ¸si r2, notat cu r1 θ r2, este definit prin:
r1 θ r2 = {(t1, t2)|t1 ∈ r1, t2 ∈ r2, t1[Aαi ]θit2[Bβi
], i = 1, k}
unde θ = (Aα1 θ1Bβ1 ) ∧ (Aα2 θ2Bβ2 ) ∧ . . . ∧ (Aαk
θkBβk
)
Daca θi este operatorul de egalitate, atunci θ-joinul se mai
numeste si equijoin.
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - θ-join, equijoin
Observat¸ie 1: un join oarecare cu condit¸ia TRUE pentru orice
combinat¸ie de tuple este un produs cartezian: r1 truer2 = r1 × r2
Observat¸ie 2: Joinul oarecare poate fi considerat ca fiind o filtrare
dup˘a anumite criterii ale rezultatelor unui produs cartezian:
r1 θ r2 = σθ(r1 × r2)
Exemplu SQL:
SELECT s.nume, p.nume FROM studenti s, profesori p
WHERE s.nume > p.nume;
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Baze de date - Algebra relat¸ional˘a
Modelul Relat¸ional
Operat¸ii pe mult¸imi ˆın modelul relat¸ional
Operat¸ii specifice algebrei relat¸ionale
Exercit¸ii
Operat¸ii ˆın algebra relat¸ional˘a - Semijoin: ¸si
Operat¸ia de semijoin stˆang selecteaz˘a acele rˆanduri din relat¸ia
aflat˘a ˆın partea stˆang˘a ( ) care au corespondent (ˆın sensul joinului
natural) ˆın relat¸ia din partea dreapta.
Formal, definim semijoinul stˆang a dou˘a relat¸ii r1 peste R1[U1] ¸si
r2 peste R2[U2] ca fiind:
r1 r2 = πU1 (r1 r2)
Deja ˆıntˆalnit la proprietat¸ile Joinului natural sub denumrea r1.
Semijoinul drept este definit similar dar preluˆand liniile din relat¸ia
aflat˘a ˆın dreapta (doar cele ce au corespondent ˆın relat¸ia din
stˆanga).
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Operat¸ii ˆın algebra relat¸ional˘a - Antijoin:
Tuplele r˘amase din relat¸ia din stˆanga (care nu au fost preluate de
semijoinul stˆang), formeaz˘a rezultatul operatorului Antijoin.
Formal, definim antijoinul stˆang a dou˘a relat¸ii r1 peste R1[U1] ¸si r2
peste R2[U2] ca fiind:
r1 r2 = r1 − πU1 (r1 r2)
. . . r1”
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Operat¸ii ˆın algebra relat¸ional˘a - Joinul la Stˆanga:
Fie r1 ¸si r2 dou˘a relat¸ii ˆın care nu toate tuplele din r1 au un
corespondent ˆın r2.
Operat¸ia Join la Stanga a celor dou˘a relat¸ii r1 ¸si r2 este reuniunea
dintre tuplele existente ˆın r1 r2 ¸si tuplele din r1 ce nu sunt
utilizate ˆın join completate cu valoarea NULL pentru atributele din
U2.
r1 r2 = r1 r2 UNION πU1U2 (r1 − πU1 (r1 r2))
Joinul la Dreapta este definit similar, de aceast˘a dat˘a preluˆand ¸si
liniile ce nu s-au folosit in Joinul natural din tabela din dreapta
(r2).
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Operat¸ii ˆın algebra relat¸ional˘a - Joinul Extern:
Operat¸ia de Join exterior cuprinde toate liniile din Joinul la Stˆanga
¸si din Joinul la Dreapta.
r1 r2 = (r1 r2) ∪ (r1 r2)
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Operat¸ii ˆın algebra relat¸ional˘a - Joinul Extern:
Exemple:
SELECT * FROM studenti LEFT JOIN profesori ON
studenti.prenume = profesori.prenume;
(Tot¸i student¸ii ¸si asociat¸i cu profesorii cu acela¸si prenume cˆand
este cazul)
SELECT * FROM studenti RIGHT JOIN profesori ON
studenti.prenume = profesori.prenume;
(Unii student¸i care sunt asociat¸i cu profesorii avˆand acela¸si
prenume ˆımpreun˘a cu restul profesorilor)
SELECT * FROM studenti FULL JOIN profesori ON
studenti.prenume = profesori.prenume;
(Student¸ii ¸si profesorii ¸si asocierile ˆıntre ei, dac˘a exist˘a)
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Notat¸ii (alternative) pentru operatorii din alg. relat¸ional˘a
Proiect¸ia (πU (r1)): r1[U]
Join natural (r1 r2): r1 ∗ r2
Join oarecare (sau theta-join): r1 θ r2
Select¸ia : σθ(r1) [obs: r1 θ r2 = σθ(r1 × r2)]
Join la stˆanga: r1 ◦ L r2
Join la dreapta: r1 ◦ R r2
Full outer join : r1 ◦ r2
Redenumirea: Dac˘a r este definit peste B1, B2, . . . , Bn ¸si vrem s˘a
redenumim numele atributelor, vom folosi operatorul de
redenumire ρ : r = ρ(r1)A1,A2,...,An - redenumirea atributelor lui r
ˆın A1, A2, . . . , An
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Exercit¸ii:
1. Pentru r1, r2 exemplificate la Joinul natural, construit¸i restul
tipurilor de Join studiate.
2. Utilizˆand schema de baze de date de la laborator, scriet¸i ˆın
algebra relat¸ional˘a expresii de select¸ie pentru urm˘atoarele:
Cursurile din facultate ˆımpreun˘a cu numele prof. ce le t¸in.
Numele ¸si prenumele student¸ilor din anul 1 ¸si care au burs˘a
mai mare de 300 ron.
Prenumele student¸ilor care au acela¸si nume de familie ca
m˘acar unul din profesori.
Numele ¸si prenumele student¸ilor, cursurile pe care le-au urmat
¸si notele pe care le-au obt¸inut.
Scriet¸i interog˘arile SQL asociate formulelor din algebra relat¸ional˘a
scrise mai sus.
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Modelul Relat¸ional
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Exercit¸ii
Bibliografie
Baze de date relat¸ionale. Dependent¸e - Victor Felea; Univ. Al.
I. Cuza, 1996
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Software
Relational
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