Advanced Database Systems Introduction

Advanced Database
Systems
Introduction
Juliet Moso
Department of Computer Science
Juliet.Moso@dkut.ac.ke
Advanced Database Systems

Basic Definitions
Database: Organized collection of logically
related data.
Data: Known facts that can be recorded and
have an implicit meaning.
 Structured: numbers, text, dates
 Unstructured: images, video, documents
Information: data processed to increase
knowledge in the person using the data
Metadata: data that describes the properties
and context of user data.
Monday, July 17, 2023
Advanced Database Systems 2

Basic Definitions
Database Management System (DBMS): A
software package/ system to facilitate the
creation and maintenance of a computerized
database.
Database System: The DBMS software
together with the data itself. Sometimes, the
applications are also included.

Why study database management?
 Critical to business, government, science, culture, society
 Determines success of many corporations (even their
existence)
 Many tech companies built on data management (Google,
Amazon, Yahoo!, Facebook, …)
 Other companies offer database products (Microsoft, IBM,
Oracle)
 Database systems span major areas of computer science
 Operating systems (file, memory, process management)
 Theory (languages, algorithms, complexity)
 Artificial Intelligence (knowledge-based systems, logic, search)
 Software Engineering (application development)
 Data structures (trees, hashtables)

Regularly Structured Data
Sets the structure once (e.g., table attributes) and then
has many instances (records) that use that structure
Examples of regularly structured data
 Employee, payroll, bank account, Data captured on web
forms
 DBMS or RDBMS mainly designed to store, manage,
and retrieve structured data
Examples of unstructured (loosely or “semistructured”)
data
 Documents, video, audio, images, maps, …
 Managed mainly by content management and
information retrieval systems

File Management Systems
A File is un-interpreted, unstructured collection
of information
File operations: delete, catalog, create, rename,
open, close, read, write, find, …
Access methods: Algorithms to implement
operations along with internal file organization
Examples: File of Customers, File of Students;
Access method: implementation of a set of
operations on a file of students or customers.

File Management System Problems
Data redundancy and inconsistency
 Multiple file formats, duplication of information in
different files
Difficulty in accessing data
 Need to write a new program to carry out each new task
Data isolation — multiple files and formats
Integrity problems
 Integrity constraints (e.g., account balance > 0) become
“buried” in program code rather than being stated
explicitly
 Hard to add new constraints or change existing ones

File Management System Problems
Atomicity of updates
 Failures may leave database in an inconsistent state with
partial updates carried out
 Example: Transfer of funds from one account to another
should either complete or not happen at all
Concurrent access needed for performance
 Uncontrolled concurrent accesses can lead to inconsistencies
 Example: Two people reading a balance (say 100) and
updating it by withdrawing money (say 50 each) at the same
time
Security problems
 Hard to provide user access to some, but not all, data

Problems with Data Redundancy
Waste of space to have duplicate data
Causes more maintenance headaches
The biggest problem:
o Data changes in one file could cause
inconsistencies
o Compromises in data integrity
9 Monday, July 17, 2023

SOLUTION:
The DATABASE Approach
Central repository of shared data
Data is managed by a controlling agent
Stored in a standardized, convenient form
10
Requires a Database Management System (DBMS)
Order Filing
System
Invoicing
System
Payroll
System
DBMS
Central database
Contains employee,
order, inventory,
pricing, and
customer data

Database Management System (DBMS)
 DBMS contains information about a particular enterprise
 Collection of interrelated data
 Set of programs to access the data
 An environment that is both convenient and efficient to use
 Database Applications:
 Banking: transactions
 Airlines: reservations, schedules
 Universities: registration, grades
 Sales: customers, products, purchases
 Online retailers: order tracking, customized recommendations
 Manufacturing: production, inventory, orders, supply chain
 Human resources: employee records, salaries, tax deductions

Typical DBMS Functionality
Define a database : in terms of data types,
structures and constraints
Construct or Load the Database on a secondary
storage medium
Manipulating the database : querying,
generating reports, insertions, deletions and
modifications to its content
Concurrent Processing and Sharing by a set of
users and programs – yet, keeping all data valid
and consistent.

Advantages of Using Databases
Controlling redundancy in data storage and in
development and maintenance efforts.
Sharing of data among multiple users.
Restricting unauthorized access to data.
Providing persistent storage for program
Objects (in Object-oriented DBMS’s)
Providing Storage Structures for efficient Query
Processing

Advantages of Using Databases
Providing backup and recovery services.
Providing multiple interfaces to different classes
of users.
Representing complex relationships among
data.
Enforcing integrity constraints on the database.
Drawing Inferences and Actions using rules

Database Users
End users
 Use the database system to achieve some goal. They use
the data for queries, reports and may update the database
content.
Application developers
 Write software to allow end users to interface with the
database system
Database systems programmer
 Writes the database software itself
 They define the content, the structure, the constraints, and
functions or transactions against the database.
 They must communicate with the end-users and understand
their needs.

DB Users: Database Administrator
Coordinates all the activities of the database system;
has a good understanding of the enterprise’s
information resources and needs.
Database administrator's duties include:
 Schema definition
 Storage structure and access method definition
 Schema and physical organization modification
 Granting user authority to access the database
 Specifying integrity constraints
 Acting as liaison with users
 Monitoring performance and responding to changes in
requirements

Data Models
A collection of tools for describing
 Data
 Data relationships
 Data semantics
 Data constraints
Relational model: Information is stored as tuples or
records in relations or tables
Entity-Relationship data model (mainly for database
design)
Object-based data models (Object-oriented and
Object-relational)
Semi-structured data model (XML)

Data Manipulation Language (DML)
Language for accessing and manipulating the data
organized by the appropriate data model
 DML also known as query language
Two classes of languages
 Procedural – user specifies what data is required and
how to get the data
 Declarative (nonprocedural) – user specifies what data
is required without specifying how to get the data
SQL is the most widely used query language
SQL Statements: SELECT, INSERT, UPDATE,
DELETE, MERGE

Data Definition Language (DDL)
Specification notation for defining the database schema
 Example: create table instructor (
ID char(5),
name varchar(20),
dept_name varchar(20),
salary numeric(8,2))
SQL Statements include:
 CREATE
 ALTER
 DROP
 RENAME
 TRUNCATE
 COMMENT

Data Definition Language (DDL)
DDL compiler generates a set of table templates
stored in a data dictionary
Data dictionary contains metadata (i.e., data about
data). It stores information about the database
itself
The dictionary holds
 Descriptions of database objects (tables, users,
rules, views, indexes,…)
 Information about who is using which data
(locks)
 Schemas and mappings

SQL
 SQL: widely used non-procedural language
 Example: Find the name of the instructor with ID 22222
select name
from instructor
where instructor.ID = ‘22222’
 Example: Find the ID and building of instructors in the Physics
dept.
select instructor.ID, department.building
from instructor, department
where instructor.dept_name = department.dept_name and
department.dept_name = ‘Physics’
 Application programs generally access databases through one of
 Language extensions to allow embedded SQL
 Application program interface (e.g., ODBC/JDBC) which allow
SQL queries to be sent to a database

Query Processor
Compiler – verifies whether a program or
query is written in accordance with DDL and
DML rules
Optimizer – Finds the most effective way to
access the required data and supply it in a
user requested form. Monitors the query
execution and modifies a query evaluation
plan if necessary

Transaction Management
A transaction is a collection of operations that
performs a single logical function in a database
application
Transaction-management component
ensures that the database remains in a consistent
(correct) state despite system failures (e.g., power
failures and operating system crashes) and
transaction failures.
Concurrency-control manager controls the
interaction among the concurrent transactions, to
ensure the consistency of the database.

Storage Management
Storage manager is a program module that
provides the interface between the low-level
data stored in the database and the application
programs and queries submitted to the system.
The storage manager is responsible for the
following tasks:
 interaction with the file manager
 efficient storing, retrieving and updating of
data.

File Manager
File Manager is responsible for mapping
logical database units (objects, relations,
etc.) into a set of low level files.
It is responsible for maintenance of files and
indexes on them. It should be able to create
and destroy index and collect unused
storage space to eliminate any unneeded
gaps on disks.

Buffer Manager
Buffer Manager is responsible for the allocation
and maintenance buffer space in memory to
facilitate processing database data by several
concurrent applications.
Buffer Manager decides when to load data from
a buffer to a database or discard the data and
under what conditions a new data should be put
into a buffer

Database Architecture
The architecture of a database system is
greatly influenced by the underlying computer
system on which the database is running:
 Centralized
 Client-server
 Parallel (multi-processor)
 Distributed

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