This document discusses the different types of keys used in database management systems (DBMS). It outlines five types of keys: super key, candidate key, primary key, foreign key, and composite key. For each key type, it provides a definition and examples to illustrate how the key uniquely identifies records in a database table. The primary points made are that super keys are the broadest unique identifiers, candidate keys are minimal super keys, primary keys must uniquely identify each record and not change, and foreign keys link records between related tables.
In DBMS (DataBase Management System), the relation algebra is important term to further understand the queries in SQL (Structured Query Language) database system. In it just give up the overview of operators in DBMS two of one method relational algebra used and another name is relational calculus.
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In DBMS (DataBase Management System), the relation algebra is important term to further understand the queries in SQL (Structured Query Language) database system. In it just give up the overview of operators in DBMS two of one method relational algebra used and another name is relational calculus.
This is the presentation file about inheritance in java. You can learn details about inheritance and method overriding in inheritance in java. I think it's can help your. Thank you.
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DBMS-Keys , Attributes and Constraints.pptxsajinis5
keys uniquely identify records;Attributes represent data characteristics, classified as simple or composite, with associated data types. Constraints maintain data integrity
### Introduction
The Entity-Relationship Model (ERM) serves as a crucial concept in the realm of database design, offering a conceptual and visual framework for organizing and structuring data within a database system. Developed by Peter Chen in 1976, this model has evolved into a fundamental tool widely employed in both academic and industrial database design.
### Core Elements: Entities and Attributes
At its essence, the ERM revolves around entities, which can be real-world objects like a person or a car, or abstract concepts such as an order or a transaction. Each entity is characterized by its attributes—properties defining the entity and specifying the type of information storable about it.
### Relationship Dynamics
Entities in the ERM are not isolated; they are interconnected through relationships, representing associations and interactions between them. These relationships are pivotal in defining the connections and dependencies between different entities within a database. They can take the form of one-to-one, one-to-many, or many-to-many, mirroring the intricate web of real-world interactions.
### Visual Representation
Graphical notations play a crucial role in ERM, employing symbols like rectangles for entities, ovals for attributes, and diamond shapes for relationships. Lines connect these symbols, creating a visual representation that simplifies comprehension for designers, developers, and stakeholders.
### Strengths of ERM
One standout feature of the ERM is its capability to model complex relationships and business rules in a straightforward and understandable manner. This simplification streamlines the database design process, allowing designers to concentrate on the logical structure of data without delving into intricate technical details. Furthermore, the model facilitates effective communication among stakeholders, ensuring a shared understanding of the data model.
### Versatility and Adaptability
ERM isn't confined to just database design—it plays a vital role in documenting existing databases and acts as a blueprint for their implementation and maintenance. As databases evolve, the ERM can be updated to accommodate changes in data structure and relationships. This adaptability makes it a valuable tool across diverse applications, including business, finance, healthcare, and education.
### Normalization and Efficiency
Normalization, closely associated with the ERM, is a process that minimizes redundancy and dependency in a database. By adhering to normalization principles, designers can create databases that are efficient, scalable, and easy to maintain. This involves breaking down complex data structures into simpler, more manageable forms, reducing the risk of data anomalies and inconsistencies.
### Limitations and Considerations
While widely used and effective, the ERM does have its limitations. It primarily focuses on the logical representation of data and may not fully capture certain aspects of a system's.
2. Here I come to my topic i.e. Keys in DBMS.
• DBMS has Five types of Keys in it and they all has different functionality.
• The Keys are as follows:
• Super Key
• Candidate Key
• Primary Key
• Foreign Key
• Composite Key
Let’s discuss one by one all of the five keys.
3. SUPER KEY
Super Key is a set of attributes whose set of values can uniquely identify an entity
instance in the entity set.
A Super Key can contains one or more than one attributes.
Super Key is the broadest definition of unique identifiers of an entity in an entity
set.
4. SUPER KEY
The combination of “SSN” and “Name” is a super key of the following entity set
customer.
Because:
The value of attributes “SSN” and “Name”, such as 558-36-1234 and
Susan, can uniquely identify that particular customer in customer entity set,
which is the pool of all customers.
Customer-name
Customer-street
customer
SSN
Customer-city
5. We are unsurprisingly very interested in the most
economical combination(s) of attributes that can
uniquely identify any particular entity.
Therefore, we introduce Candidate Key next.
6. CANDIDATE KEY
Candidate key is a set of one or more attributes whose set of values can
uniquely identify an entity instance in the entity set.
Any attribute in the candidate key cannot be omitted without destroying the
uniqueness property of the Candidate key.
It is minimal Super Key.
7. CANDIDATE KEY
While most entity sets have only one candidate key, some entity sets could
have more than one candidate key.
Candidate key could have more than one attributes.
In building a database in a database software, the software will only allow to
use one candidate key to be the unique identifier of an entity for an entity set.
Properties of Candidate Key…..
8. CANDIDATE KEY
• Example:
• (SSN, Name) is NOT a candidate key, because taking out “name” still leaves “SSN”
which can uniquely identify an entity. “SSN” is a candidate key of customer.
• Example: Both “SSN” and “License #” are candidate keys of Driver entity set.
Customer-name
Customer-street
customer
SSN
Customer-city
9. Overall, Super Key is the broadest unique identifier; Candidate Key is a
subset of Super Key; and Primary Key is a subset of Candidate Key.
In practice, we would first look for Super Keys. Then we look for Candidate
Keys based on experience and common sense.
If there is only one Candidate Key, it naturally will be designated as the
Primary Key.
If we find more than one Candidate Key, then we can designate any one of
them as Primary Key.
10. PRIMARY KEY
The Primary Key is an attribute or a set of attributes that uniquely identify a specific
instance of an entity.
Every entity in the data model must have a primary key whose values uniquely identify
instances of the entity.
11. To qualify as a primary key for an entity, an attribute must have the
following properties:
It must have a non-null value for each instance of the entity
The value must be unique for each instance of an entity
The values must not change or become null during the life of each entity instance
PRIMARY KEY
Properties Of Primary Keys....
12. Primary and Foreign keys are the most basic
components on which relational theory is based.
Each entity must have a attribute or attributes, the
primary key, whose values uniquely identify each
instance of the entity. Every child entity must have
an attribute, the foreign key, that completes the
association with the parent entity.
13. FOREIGN KEY
A Foreign key is an attribute that completes a relationship by identifying the parent
entity.
Foreign keys provide a method for maintaining integrity in the data (called referential
integrity) and for navigating between different instances of an entity.
Every relationship in the model must be supported by a foreign key.
14. FOREIGN KEY
Every dependent and category (subtype) entity in the model must have a
foreign key for each relationship in which it participates.
Foreign keys are formed in dependent and subtype entities by migrating the
entire primary key from the parent or generic entity. If the primary key is
composite, it may not be split.
Properties Of Foreign Key….
15. COMPOSITE KEY
When a primary key is created from a combination of 2 or more columns, the
primary key is called a composite key.
Each column may not be unique by itself within the database table but when
combined with the other column(s) in the composite key, the combination is
unique.