Database system concepts and architecture Winter 2007Ron McFadyen ACS-39021 Database schema Database system architecture Data independence concept Database

Winter 2007 Ron McFadyen ACS-3902 1

Database system concepts and architecture

•Database schema

•Database system architecture

•Data independence concept

•Database language

•Database application

•Interfaces

•Database environment

Ch 2



Schema: a description of a database -- meta data

•the intension of the database

Schema evolution: if the database definition changes, we say it evolves.

Database State: the data in the database at a particular point in time

•the extension of the schema



Sample database

Student Name StNo Class Major

Smith 17 1 CS

Brown 8 2 CS

Course CName CNo CrHrs Dept

Database 8803 3 CS

C 2606 3 CS

Section SId CNo Semester Yr Instructor

32 8803 Spring 2000 Smith

25 8803 Winter 2000 Smith

43 2606 Spring 2000 Jones

Grade StNo SId Grade

17 25 A

17 43 B



University database schema:

Course

Cnamestring(20)

CNo string(20)

CrHrs integer

Dept.String(20)

GradeStNo integer

SId integer

GradeString(20)

Student

Name string(20)

StNo integer

Class integer

Major String(20)

SectionSID integer

CNo string(20)

Semester integer

Yr integer

Instructor string(20)



Schema evolution:

Course

Cnamestring(20)

CNostring(20)

CrHrs integer

Dept.String(20)

Student

Name string(20)

StNo integer

Class integer

Major String(20)

PrerequisiteCNo string(20)

Pre-CNo string(20)… ...

new table added



Schema evolution:

Course

Cnamestring(20)

Cnostring(20)

CrHrs integer

Dept.String(20)

Student

Name string(20)

StNo integer

Class integer

Major String(20)

Age integer

Sex string(20)… ...

new attributes added



Sample database


Smith 17 1 CS

Brown 8 2 CS


Database 8803 3 CS

C 2606 3 CS




43 2606 Spring 2000 Jones

Grades StNo Sid Grade

17 25 A

17 43 B



Database state changed:


Smith 17 1 CS

Brown 8 2 CS


Database 8803 3 CS

C 2606 3 CS




Grades StNo Sid Grade

17 25 A

17 43 B



Definition

Manipulation

Construction

We define the database

database state is the empty state with no data

initial state when database is populated (loaded)

current state changes with each insert, delete, update

hopefully, the database goes from one correct/valid state to another



Three-schema architecture

Externalview

Externalview

Conceptualschema

Internalschema

Physical storage structures and details

Describes the whole database for all users

A specific user or groups view of the database



Data independence

Ability to change the database at one level with no impact to the next higher level

•physical data independence - the ability to change the physical schema without affecting the conceptual schema

•typical example: add a new index

•logical data independence - the ability to change the conceptual schema without affecting existing external views or application programs

•typical example: add an attribute



DBMS Languages

Data definition language (DDL): used to define the database schema. Ideally one schema definition language per level

•in practice there might be one DDL for all levels



DBMS Languages

Data Manipulation language (DML): Used to manipulate data.

•typical systems provide a general purpose language for inserting, updating, deleting, and retrieving data

•two distinctions: set-oriented and row-at-a-time



EXEC SQL DECLARE C1 CURSOR FORSELECT au_fname, au_lname FROM authors FOR BROWSE;EXEC SQL OPEN C1;while (SQLCODE == 0){EXEC SQL FETCH C1 INTO :fname, :lname;}

Database applicationsIf an application program that accesses the database embeds DML commands within it, then we have a host language and a data sublanguage.



Record-at-a-time

•procedural - need loops, etc

•navigate through data obtaining 1 record at a time

•note that SQL does permit this via cursors

Set-oriented operations

•select Name, StNo from student where Name like “M%”

•EXEC SQL DELETE FROM authors WHERE au_lname = 'White'



DBMS interfaces

•menu-based

•forms-based

•GUI

•natural language

•for dba



Example of a menu-based interface: from MS Access



DBMS environment

see figure 2.3•stored data manager

A module to control access to DBMS information that is stored on disk, whether it is part of the database or the catalog.

•DDL compiler

A module to process schema definition, specified in the DDL, and store description of the schema (meta-data) in the DBMS catalog.

•DML compiler

It translates the DML commands into object code for database access.•run-time database processor

It handles database access at run time; it receives retrieval or update operations and carries them out on the database.



DBMS environment

•query compiler

It handles high-level queries that are entered interactively. It parses, analyzes, and compiles or interprets a query by creating database access code, and then generates calls to the rum-time processor for executing the code.

•pre-compiler

It extracts DML commands from an application program which is written in host programming language like C, Pascal, etc.



DBMS utilities•loading

loading existing files - such as text files or sequential files - into the database.

•backup

creating a backup copy of the database, usually by dumping the entire database into tape.

•file reorganization

reorganizing a database file into a different file organization to get a better performance.

•performance monitoring

monitoring database usage and providing statistics to the DBA.



DBMS Architectures

•centralized

•client/server

2-tier

3-tier



DBMS Architectures

•centralized

Displaymonitor

Displaymonitor

…

hardware

Software: dbms, applications, …

OS



DBMS Architectures

Client Server

ApplicationServer

Db Server Client

2-tier client/server: software components are distributed across two systems

3-tier client/server

User interface

Application or web server

DBMS



Classifying DBMSs

data model:

relational / object-oriented / hierarchical / network / object-relational

users: single-user / multi-user

location: distributed / centralized

cooperation: homogeneous / heterogeneous

OLTP: on-line transaction processing

•used to run the day-to-day operations of a business

•event-oriented: take an order, make a reservation, payment for goods, withdraw cash, ...

Documents

Database system concepts and architecture Winter 2007Ron McFadyen ACS-39021 Database schema Database system architecture Data independence concept Database