Data Management I

DBMS

Relational Systems

Overview Introduction DBMS

– components– types

Relational Model– characteristics– implementation

Physical Structure

File-based Systems

Collection of applications that performs services for end user- programs define and manage data

Limitations– Data dependence-structure defined in program– Incompatible file formats– Programs written to satisfy function

Database Definition

A database system is essentially a computerized record keeping system whose overall purpose is to maintain information and make it available on demand

Advantages of Database REDUCED REDUNDANCY - Controlling duplication INTEGRATION AND SHARING OF DATA - One set of data to

maintain MAINTAINING CONSISTENCY - Data propagation DATA ACCESS - Multiple access paths; High level language STANDARDIZATION - Enforcing local and global standards SECURITY - User access; Protection of Data DATA INDEPENDENCE - Data descriptors separate from

application program Increased integrity and concurrency control

Components of a Database System Data

– Note: Date uses data and information interchangably Hardware

– Processor, main memory, secondary storage and I/O devices– Individual PC to a network of computers

Software– DBMS– Application programs– Others software tools

Users– Application Programmers– End - Users– DBA’s

Procedures ??

Database Management SystemDBMS

Software Software Components

– Data Definition DDL source form object form

– Data manipulation DML planned request unplanned request

– Data administration DAL Data security and recovery

– Integrity and concurrency– Performance– Data dictionary

Data DictionaryCatalog Repository

Database of information about a database

– description of all database objects

– references to all users of the database

– references to all programs and transactions that access the database

Provides the description of the data to enable program-data independence

Database Models Hierarchical - IMS

– tree structure with predefined access paths

– child has one parent Network - CODASYL - IDMS

– multiple paths to same record Multi-dimensional Object-oriented

– data and methods

– highly-variable structure

– tightly coupled with programming language Hybrid - Object/Relational Databases

Relational Model

Evolving System - System designed by Codd, partially implemented, developing

Theoretical Vs Available - No system met Codd’s original 12 rules. Degrees of relational defined

Date’s work - Supportive of relational model but not always in agreement with Codd

Functions of a DBMS Data Storage, Retrieval and Update.

– Must furnish users with the ability to store, retrieve, and update data in the database.

A User-Accessible Catalog.– Must furnish a catalog in which descriptions of data

items are stored and which is accessible to users. Transaction Support

– Must furnish a mechanism to ensure that either all the updates corresponding to a given transaction are made or that none of them are made.

Functions of a DBMS Concurrency Control Services

– Must furnish a mechanism to ensure that database is updated correctly when multiple users are updating the database concurrently.

Recovery Services– Must furnish a mechanism for recovering the database

in the event that the database is damaged in any way.

Authorization Services– Must furnish a mechanism to ensure that only

authorized users can access the database.

Functions of a DBMS Support for Data Communication

– Must be capable of integrating with communication software.

Integrity Services– Must furnish a means to ensure that both the data in the

database and changes to the data follow certain rules.

Services to Promote Data Independence– Must include facilities to support the independence of

programs from the actual structure of the database.

Utility Services– Should provide a set of utility services.

ANSI/SPARC Architecture

...EXTERNAL LEVEL(individual userview)

CONCEPTUAL LEVEL(community user view)

INTERNAL LEVEL(storage view)

External Level

Users’ view of the database Language

– Application programmer– End-user

External View– Logical record– Data authorized to view

External Schema

Conceptual Level

Community view of database Representation of entire information

content Conceptual schema

– definition of total database content ++– data independent

Internal Level

Low-level representation of entire database– occurrences

Describes how the data is stored in the database

Not physical level Level used by utilities to increase

performance.

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Differences between Three Levels of ANSI-SPARC

Architecture

Data Independence and the ANSI-SPARC Three-level Architecture

Data Model

Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization.

Data Model comprises:– A structural part

– A manipulative part

– Possibly a set of integrity rules

Data Models Object-based Data Models

– Entity-Relationship– Semantic– Functional– Object-Oriented

Record-based Data Models– Relational Data Model– Network Data Model– Hierarchical Data Model

Physical Data Models

Client/Server

Client/server model naturally fits the architecture

Front end Back end Middleware

Client/Server

Front End

GUI Applications Fat vs thin client Should any data

be stored in front end?

Back EndServer

Data Shared DBMS Database information Fat server vs thin server Should server contain

applications?

Middleware

Enables front end to speak to back end. Middleware can be as simple as API’s and

as complex as Tuxedo software Determinants

– variety of databases– networks– size

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Summary of Client-server Functions