Chapter 1 Introduction

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• Chapter 1Introduction

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Introduction

• Definition A database management system (DBMS)
  is a general-purpose software system that
  facilitates the process of defining,
  constructing, and manipulating databases for
  various applications.
• Definition A database is a collection of related
  data.
• Definition Data are known facts that can be
  recorded and that have implicit meaning.
• Definition File processing systems are business
  computer systems which store groups of records
  in separate files used to process business
  records produce information.

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Introduction
DBMS File Processing
Systems
Data is often duplicated causing higher storage
and access cost, poor data integrity, and data
inconsistency
- Data redundancy inconsistency
Reduced by ensuring a physical piece of data
is available to all programs
- Accessing data
Allow flexible access to data (e.g., using
queries for data retrievals)
Allow pre-determined access to data (i.e.,
complied programs) application programs
are dependent on file formats
- Concurrent access
Designed to coordinate multiple users
accessing the same data at the same time
Designed to allow a file to be accessed by two
programs concurrently only if both programs have
read-only access to the file
High, enforced
Loose, not enforced
- Data security integrity
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Data Abstraction

• Provides an abstract view of data
• Physical level the lowest level of abstraction
  describes the storage structure of data.
• Conceptual level the next-higher level of
  abstraction describes the logical structure of
  the database.
• View level the highest level of abstraction
  describes part of the entire database. Many
  views are provides for the same database.

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Database Terminology

• Database Schema or Conceptual View describes
  the overall logical structure of the entire
  database
• Database Instance describes the content of the
  database
• Schema Type,

Instance Value of a variable
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Data Independence

• The capacity to change the schema definition at
  one level without having to change the schema
  definition at the next higher level
• Physical data independence capacity to change
  the physical schema without having to rewrite
  the application programs
• Logical data independence capacity to change
  the conceptual schema without having to
  rewrite the application programs
• logical data independence is more difficult to
  achieve than physical data independence

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Data Models

• Describe relationships among data, data
  semantics, integrity, and semantic constraints
  at the conceptual and view levels
• I. Object-Based Logic Models
• DB is structured in variable-length records
• Provide flexible structuring capabilities
• Allow explicit specifications of data constraints
• Widely used data models Entity-Relationship and
  Object-Oriented
• II. Record-Based Logical Models
• DB is structured in fixed-format records of
  different types
• Three widely used data models Relational,
  Hierarchical, and Network
• II. Semi-Structured Data Model
• Data items of the same type can have different
  sets of attributes
• Widely used data model XML (Extensible Markup
  Language)

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Entity-Relationship (E-R) Model

• An object-based Model
• A graphical structure (Chapter 7)
• Widely used in database design
• Consists of real world objects called entities
  and relationships among entities
• An entity is an distinguishable object with a set
  of attributes
• Entity set is a set of entities of the same type
• Relationship set is a set of relationships of the
  same type
• Mapping cardinalities represent the associations
  among different entities

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An Entity-Relationship Diagram
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An Entity-Relationship Diagram
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The Object-Oriented Model

• An object-based Model
• Object identity (object-based) vs. value identity
  (record-based)
• A collection of objects with unique identities
• Objects can be simple, complex, or made up of
  other objects
• Objects contain methods, i.e., codes operated on
  objects
• An operation/function can be performed on objects
  of particular classes
• Provide public interface for objects of a
  particular class
• Classes consist of objects
• Correspond to abstract data type (ADT)
• Users can define their own classes
• Only way to operate on an object by means of
  operators defined
• Message passing for accessing data in different
  objects
• Apply a given method to a given object by sending
  a message

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Object-Oriented Database Systems
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The Relational Model

• A record-based Model
• Data are organized and stored into 2-dimensional
  tables (called relations)
• Flexible to use and easy to understand
• A relational database schema consists of a number
  of relation schemas of the form R(A1, A2, ,
  An), where R is a relation name and Ai, 1 lt i lt
  n, is an attribute name.

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The Relational Model
Relational term
Informal equivalence
Relation
Table
Tuple
Row/Record
Cardinality
of rows
Attribute
Column/Field
Degree
of columns
Set of legal values
Domain
Unique Identifier
Primary Key
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The Relational Database Model
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Data Definition Languages (DDL) Data
Manipulation Languages (DML)

• DDL
• Declares the DB schema and compiles the schema
  into tables
• DML
• Access/Manipulate (retrieve, insert, delete,
  modify) the DB
• Procedural (or descriptive) specify what is
  needed and how to get it
• Non-procedural (or declarative) specify what is
  needed but not how to get it

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Overall System Structure