Chapter 14

Databases

Understand a Understand a DBMSDBMS and define its components. and define its components.

Understand the architecture of a DBMS and its levels.Understand the architecture of a DBMS and its levels.

Distinguish between different Distinguish between different database modelsdatabase models..

Understand the concept of Understand the concept of relational databaserelational database operations operationson a relation.on a relation.

After reading this chapter, the reader should After reading this chapter, the reader should be able to:be able to:

OOBJECTIVESBJECTIVES

Use Use Structured Query Language (SQL)Structured Query Language (SQL) to define simple to define simplerelations. relations.

DATABASEDATABASEMANAGEMENTMANAGEMENT

SYSTEMSYSTEM

14.114.1

DBMS Database – a collection of data that is logically

coherent. DBMS – Database Management System

defines, creates, and maintains a database. Allows users controlled access to data in the database. A combination of 5 components:

Hardware Software Data Users Procedures

Figure 14-1 DBMS components

Hardware – the physical computer system that allows physical access to data.

Software – the actual program that allows users to access, maintain, and update physical data.

Data – stored physically on the storage devices Users –

End users - Normal user and DBA (Database Administrator) Application programs

Procedures – a set of rules that should be clearly defined and followed by the users.

ARCHITECTUREARCHITECTURE14.214.2

Figure 14-2Database architecture

Architecture Internal level –

Determines where data are actually stored on the storage device.

Low-level access method

Conceptual level – Defines the logical view of the data The main functions of DBMS are in this level.

External level – Interacts directly with the user. Change the data coming from the conceptual level to

a format and view that are familiar to the users.

DATABASEDATABASEMODELSMODELS

14.314.3

Database models

A database model defines the logical design of data.Describes the relationships between different

parts of data. 3 models

Hierarchical modelNetwork modelRelational model

Figure 14-3 Hierarchical model

Data are organized as an upside down tree. Each entity has only one parent but can have

several children.

Figure 14-4 Network model

The entities are organized in a graph. Some entities can be accessed through several

paths.

Figure 14-5 Relational model Data are organized in two-dimensional tables called

relations. The tables are related to each other. The most popular model.

RELATIONALRELATIONALMODELMODEL

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Relational model

RDBMS (Relational Database Management System) external view

The data are represented as a set of relations. A relation is a two-dimensional table.

This doesn’t mean that data are stored as tables; the physical storage of the data is independent of the way the data are logically organized.

Figure 14-6Relation

Name – each relation in a relational database should have a name that is unique among other relations.

Attribute – each column in a relation. The degree of the relation – the total number of attributes for a relation.

Tuple – each row in a relation. The cardinality of the relation – the total number of rows in a relation.

OPERATIONSOPERATIONSONON

RELATIONSRELATIONS

14.514.5

Operations on relations In a relational database, we can define several operations

to create new relations out of the existing ones. Basic operations:

Insert Delete Update Select Project Join Union Intersection Difference

Figure 14-7 Insert operation

An unary operation. Insert a new tuple into the relation.

Figure 14-8 Delete operation

An unary operation. Delete a tuple defined by a criterion from the relation.

Figure 14-9 Update operation

An unary operation. Changes the value of some attributes of a tuple.

Figure 14-10 Select operation

An unary operation. It is applied to one single relation and creates another

relation. The tuples in the resulting relation are a subset of the tuples

in the original relation. Use some criteria to select

Figure 14-11 Project operation An unary operation. It is applied to one single relation and creates another

relation. The attributes in the resulting relation are a subset of the

attributes in the original relation.

Figure 14-12 Join operation A binary operation. Combines two relations based on common attributes.

Figure 14-13 Union operation

A binary operation. Creates a new relation in which each tuple is either in the

first relation, in the second, or in both. The two relations must have the same attributes.

Figure 14-14 Intersection operation

A binary operation. Creates a new relation in which each tuple is a member in

both relations. The two relations must have the same attributes.

Figure 14-15 Difference operation A binary operation. Creates a new relation in which each tuple is in the first

relation but not the second. The two relations must have the same attributes.

STRUCTUREDSTRUCTUREDQUERYQUERY

LANGUAGELANGUAGE

14.614.6

SQL (Structured Query Language)

Standardized by ANSI and ISO for use on relational databases.

It is a declarative (not procedural) language, which means that the users declare what they want without having to write a step-by-step procedure.

First implemented by Oracle in 1979. SQL allows you to combine the following

statements to extract more complex information from database.

Insert

insert into RELATION-NAMEvalues ( … , … , … )

insert into COURSESvalues ( “CIS52”,”TCP/IP”, 6 )

Delete

delete from RELATION-NAMEwhere criteria

delete from COURSESwhere No=“CIS19”

Update update RELATION-NAMEset attribute1=value1, attribute2=value2, … where criteria

update COURSESset Unit=6where No=“CIS51”

Select

select *from RELATION-NAMEwhere criteria

select *from COURSESwhere Unit=5

Project

select attribute-listfrom RELATION-NAME

select No, Unitfrom COURSES

Join

select attribute-list from RELATION1,RELATION2where criteria

select No,Course-Name,Unit,Professorfrom COURSES,TAUGHT-BYwhere COURSES.No=TAUGHT-BY.No

Union select *from RELATION1unionselect *from RELATION2

select *from CIS15-Rosterunionselect *from CIS52-Roster

Intersection select *from RELATION1intersectionselect *from RELATION2

select *from CIS15-Rosterintersection select *from CIS52-Roster

Difference select *from RELATION1minusselect *from RELATION2

select *from CIS15-Rosterminusselect *from CIS52-Roster

OTHEROTHERDATABASEDATABASE

MODELSMODELS

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Distributed databases

It is not a new model. It is based on relational model. The data are stored on several computers that

communicate through the Internet or some private WAN.

Data are either fragmented, with each fragment stored at one site, or data are replicated at each site. Fragmented distributed databases Replicated distributed databases

Object-Oriented databases

Some application like to see data as a structure such as a record made of fields.

Tries to keep the adv. of the relational model and allows applications to access structured data.

In an OODB, objects and their relations are defined. In addition, each object can have attributes that can be expressed as fields.