CIS 507Database Programming

Database Concepts

DBMS Models

2

DatabaseA DATABASE is an organized collection of related data McFadden-Hoffer

– a shared collection of logically related data– designed to meet the information needs of multiple users in an organization

Kroenke– a self-describing collection of integrated records

self-describing: in addition to the user’s source data, contains a description of its own structure

collection of integrated records: user data, metadata (data about data), indexes to represent relationships among data and improve performance, data about applications that use the database

Rob-Coronel– a shared integrated computer structure that houses a collection of

end-user data--i.e. raw facts of interest to the end-user metadata through which the data are integrated

3

File Management Systems

The predecessor to the modern database management system

Problems

– Maintenance: Data created, managed, and accessed primarily through 3GL (COBOL, PL/I)

– Data dependent: all components sensitive to changes made to data structure or storage and retrieval methods

– Data Redundancy: uncontrolled duplication of data Data Inconsistency

Data Anomalies

– Sharing: inconsistent standards made it impossible to share data

4

DBMS

A Database Management System (DBMS) is general purpose software and hardware facility to:

– Create, delete, reorganize, and manipulate data in a database– Store, retrieve, share, and maintain data in a database– Maintain relationships between the database components– Provide security and procedures relating to privilege and access.– The integrity of all the updates and transactions that are carried out.– interface for the access, deletion and addition of data and for redefining

the relationships within the database.

A DBMS is a collection of programs that manages the database structure and controls access to the data stored in the database.

5

DBMS Disadvantages

DBMSs are complex; Need for explicit backup and

control; Costs associated with development

and operation can be substantial; Consolidation of an entire business’

information resources can create a high level of vulnerability.

6

The Database System Environment

Hardware: computer, storage, networks, devices Software: OS, DBMS, Applications, Untilities People:

– System Administrator– Database Administrator– Database Designers– Systems Analysts and Programmers– End-Users

Procedures Data

7

Database Systems Types

Number of Users: – Single-user: usually desktop– Multi-user: workgroup (small); enterprise (large)

Location:– Centralized: all data stored in a database at a single site– Distributed: database is distributed across several sites

Type and Use:– Production (transactional): designed to support day-to-day use– Decision Support: designed to make tactical and strategic decisions at middle-

and high-management levels– Decision Support Systems (data warehouse): use of historical data from many

sources to make decisions such as pricing, sales forecasts, marketing positioning (e.g. structural estimates for insurance by underwriters)

8

DBMS Functions Data Dictionary Management Data Storage Management--Data Storage Definition Language (DSDL) Data Transformation and Presentation Database Control Language (DBCL)

– Security Management– Multi-User Access Control

Backup and Recovery Management Data Integrity Management Data Access Languages

– Data Definition Language (DDL)– Data Manipulation Language (DML)

Application Program Interfaces– COBOL, C, PASCAL, Visual Basic– Administrative Utilities

Data Communication Interfaces– queries, reports, email through web browsers

9

Features of a good DBMS Open ended--can be extended Flexible--can be changed Efficient Easy to use Security should be built-in. Data independence

10

Models

A database is a model of a user’s model of reality (Kroenke)

Many different types of models involved in databases

ANSI/SPARCConceptual ModelExternal ModelInternal ModelPhysical Model

RealityObjects, Properties, RelationshipsUnique Identifier

11

ANSI/SPARC ArchitectureAmerican National Standards Institute/Standards Planning and Requirements Committee

External Model(end-user views)

Conceptual Model(Database Administrator View)

Physical Model(storage view)

Internal Model(end-user views)

12

Conceptual Model

Global view of data Enterprise-wide view as seen by DBA Conceptual schema

– basic blueprint for the database design– frequently represented with E-R diagrams

Hardware and software independent

13

External Model

Accessed by– Application programmer– End-user

External Schema– User’s authorized view of the data– A subset of the Conceptual Schema or a logical

view of the Conceptual Schema Hardware Independent; software dependent

14

Internal Model

Implementation of Conceptual Schema– Hierarchical Model DBMS– Network (CODASYL) Model DBMS– Relational Model DBMS– Object-Oriented Model DBMS– Semantic Model DBMS

Hardware independent; software dependent

15

Physical Model

Description of how data is to be stored– Definition of physical storage devices– Definition of physical access methods

Hardware and software dependent

16

Modeling Reality

Common Conceptual Modeling Terms:– Entity: a person, place, event, or thing for which data is to be collected– Attributes: properties or characteristics of an entity which describe the entity in the

context of interest– Identifier: a means of distinguishing one entity from another– Entity Class: a collection of all entities of the same type, i.e. entities that have exactly

the same properties– Relationship: an association among entities in the same or different classes

Internal Modeling Terms: unique to Internal (implementation) model– Hierarchical– Network (CODASYL)– Relational– OODBMS

Semantic Physical Model: strategy for storage and access is unique to the internal model

17

Relationships

One-to-Many– Advisor may have many Advisees– Advisee has but one Advisor (our choice)

Many-to-Many– Instructor may have many Students– Student may have many Instructors

One-to-One– Faculty is assigned to one office– An office is assigned to one faculty

INSTRUCTOR STUDENT

ADVISOR ADVISEE

FACULTY OFFICE

18

Data Integrity Constraints

Measures taken to ensure data is accurate Business Constraints: rules that must be satisfied for the business

– example: managers vacation days shall not exceed 20 Entity Integrity Constraint: there is an attribute of the entity that is used to

uniquely identify that entity– example: student id or ss#

Static Domain Constraint: a value for a property can only be one of the items in a predefined list

– example: faculty may only be instructor, assistant professor, associate professor, professor

Referential Integrity Constraint: in a one-to-many association, an entity on the many side must be associated (reference) an entity on the one side

– example: in an advising relationship, a student’s advisor must be a faculty member

19

Data Independence

Physical Data Independence:– Application programs and terminal activities remain

logically unimpaired whenever any changes are made in either storage representation or access methods.

Logical Data Independence: – Application programs and terminal activities remain

logically unimpaired when information preserving changes of any kind are made to the conceptual design

20

Hierarchical Model

Entity Segment Entity Class Segment type Attributes: Fields Identifier Value-bearing field or disk address

reference Relationships

– Conceptual Model--1-1 and 1-many in parent- child relationship; some support for two parents for same child

– Physical Model--uses child/twin pointer strategy for 1-many Data Access 3GL products--COBOL, PL/I, C, Pascal Commercial Products IMS (DL/I) and Focus

21

DBMS Models - Hierarchical

A cruise ship reservations system

MiamiMiamiMiamiMiami Los AngelesLos AngelesLos AngelesLos Angeles New YorkNew YorkNew YorkNew York

QE 2QE 2QE 2QE 2 The OrianaThe OrianaThe OrianaThe Oriana

A-1A-1A-1A-1 A-2A-2A-2A-2

April 15April 15April 15April 15

Ports ofDeparture

Namesof Ships

SailingDates

CabinNumbers

The Love BoatThe Love BoatThe Love BoatThe Love Boat

May 30May 30May 30May 30 July 15July 15July 15July 15

A-3A-3A-3A-3

The only way into the system is via the port, searching for ships or dates is inefficient - very rigid and inflexible.

22

Hierarchical Model

Advantages– Common database makes sharing practical– Security is provided and enforced– Supports some data independence– Referential integrity maintained through parent-child

relationship– Very efficient for data models that are hierarchical

(one-to-many)– Many hierarchical type applications are on mainframes

23

Disadvantages– Knowledge of physical level required– Does not support logical data independence and does not

support all physical data independence operations– Not all problems are one-to-many types– Problems with multiple parent implementation– Problems with anomalies for parent deletion– Application development in 3GL time-consuming– Support programs are not part of the DBMS– “System created by programmers for programmers!”

Hierarchical Model

24

Network (CODASYL) Model

Entity Record Entity Class Record type Attributes: Data items Identifier Value-bearing field or disk address reference Relationships

– Conceptual Model--1-1 and 1-many in owner-member set relationship; some provide elementary many-to-many relationships

– Physical Model--same type records: doubly-linked, ringed structure owners: additional references to first & last associated member in each set members: additional references to associated owner in each set

Data Access 3GL products--COBOL, PL/I, C, Pascal Commercial Products DBMS-10, IDMS (Cullinet), IDS (Honeywell),

TOTAL, IMAGE, MDBS-III

25

DBMS Models - NetworkA college class scheduling systemA college class scheduling system

D. Barry D. Rather

Student A

Courses

Instructors

Students

R. DeNiro

Student B Student C

TV 210Film 200Journalism 101

Student D Student E

Here the relationships are much more flexible but the complexity of link management makes this approach unwieldy and slow.

26

Network Model

Advantages– Can be used to directly implement one-to-one, one-to-

many, and some many-to-many relationships– Access, navigation is superior to hierarchical model– Enforces referential integrity through owner-member

relationship– Achieves some physical data independence

27

Network Model

Disadvantages– Difficult to design and use– Does not support logical data independence– Very complex--not for the novice– Navigation is achieved at the record level

28

Relational Model

Entity Row (Tuple) Entity Class Table (Relation) Attributes: Column (?dimension?) Identifier Value-bearing field or generated value Relationships

– Conceptual Model--1-1 and 1-many relationships– Physical Model--uses foreign key to link parent to child

Data Access– 4GL-- SQL– 3GL products--COBOL, PL/I, C, Pascal

Commercial Products ACCESS, ORACLE, DB2, SQL/DS, RBASE 500, INGRES, SYBASE

29

Relational Database Structure

0970000 Joe Bloe ...

0970010 Julie King ...

0970015

0970012

Anne Oether

John Smith

0970035 John Smith

...

...

...

MIS1100

MIS1150

Information Systems

Business Statistics

...

...

MIS1100 ...

...

MIS1150

...

...

...

MIS1100

MIS1100

MIS1150

MIS1150

0970000

0970000

0970010

0970015

0970012

0970035 ...

Unit Table

Unit_StudentRelationship Table

Student Table

Data relating to the relationship is stored in the relational table. Recording the semester of enrolment, marks, and the grade for each student along with the relationship places logically related data in one location.

30

Relational Model

Advantages User can focus on only the logical view Powerful query capabilities from 4GL—SQL Ad hoc query capability Aggregate processing as opposed to record at a time Standardization of language Creation, management, and data manipulation

language Easier to make changes to the logical design without

affecting applications (Logical Data Independence)

31

Relational Model

Disadvantages More powerful computers are needed because so

much is done for the user Ease of use creates a false sense of security in the

area of design