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2013-01-21 1 Silvia Stefanova, UDBL - IT - UU

DATABASE DESIGN I -

1DL300

Spring 2013

An Introductory Course on Database Systems

http://www.it.uu.se/edu/course/homepage/dbastekn/vt13/

Uppsala Database Laboratory

Department of Information Technology, Uppsala University, Uppsala, Sweden

(36)

2013-01-21 2 Silvia Stefanova, UDBL - IT - UU

Introduction to Database Technology

Elmasri/Navathe ch 1-2 Padron-McCarthy/Risch ch 1

Sobhan Badiozamany Silvia Stefanova

Department of Information Technology Uppsala University, Uppsala, Sweden

(37)

2013-01-21 3 Silvia Stefanova, UDBL - IT - UU

Outline

1. Data Model, Database Schema

• Categories of data models

• Database schemas and instances

2. Data Independence

• Three-schema architecture

• Logical independence

• Physical independence

3. Database Languages

4. Classification of DBMS 5. To Summarize

(38)

2013-01-21 4 Silvia Stefanova, UDBL - IT - UU

Outline

1. Data Model, Database Schema

• Data models, categories of data models

• Database schemas and instances

2. Data Independence

• Three-schema architecture

• Logical independence

• Physical independence

3. Database Languages

4. Classification of DBMS 5. To Summarize

(39)

2013-01-21 5 Silvia Stefanova, UDBL - IT - UU

Data Model ???

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2013-01-21 6 Silvia Stefanova, UDBL - IT - UU

Data Model

• Data Model: A collection of concepts that can be used to describe the structure of database

• Data Model consists of

oSet of concepts: data types, relationships, constraints

oSet of basic operations for specifying retrievals and updates on the database

• Every database has a data model which makes it

possible to “hide” the physical representation of data

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2013-01-21 7 Silvia Stefanova, UDBL - IT - UU

Categories of data models

• High-level (conceptual) : close to how users perceive data

oER (Entity-Relationship) model

• Low-level (physical): details of how data is stored on computers

• Representational (implementation): in between conceptual and physical

o Relational (ORACLE, DB2, SQL Server, MySQL, Mimer) o Object-oriented (ObjectStore, Objectivity, Versant, Poet) o Object-relational (Informix, Odapter, DB2)

o Hierarchical (IMS) o Network (IDMS)

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2013-01-21 8 Silvia Stefanova, UDBL - IT - UU

What is the difference between

database and database description ?

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2013-01-21 9 Silvia Stefanova, UDBL - IT - UU

Database Schema and Instances

• Database schema: the database description specified during the database design and not expected to change

• The actual data in the database may change frequently

• Database instance (state): the data in the database at a particular moment. Every change of data creates a new instance of the database.

oValid state: satisfies the structure and constraints in the database schema

oMeta-data: description of the schema (data about data)

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2013-01-21 10 Silvia Stefanova, UDBL - IT - UU

Outline

1. Data Model, Database Schema

• Categories of data models

• Database schemas and instances

2. Data Independence

• Three-schema architecture

• Logical independence

• Physical independence

3. Database Languages

4. Classification of DBMS 5. To Summarize

(45)

2013-01-21 11 Silvia Stefanova, UDBL - IT - UU

Three-schema Architecture

Conceptual schema

Database instance Internal level Conceptual level

External level End users

view1

view2

… … …

viewn

Internal schema

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2013-01-21 12 Silvia Stefanova, UDBL - IT - UU

Three-schema Architecture

• Internal level

oDescribed the physical storage structure of the database oUses a physical data model (internal schema)

• Conceptual level

oDescribes the structure of the whole database for community of users; describes entities, data types, relationships, user

operations

oUses a representation data model

• External (view) level

oDescribes the part of the database that a particular user group is interested in; hides the rest from that group

oHas a number of external schemas

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2013-01-21 13 Silvia Stefanova, UDBL - IT - UU

What is the goal with

the three-schema architecture?

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2013-01-21 14 Silvia Stefanova, UDBL - IT - UU

Data Independence

• Data Independence: The capacity to change the

schema at one level of a database system without

having to change at the next higher level

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2013-01-21 15 Silvia Stefanova, UDBL - IT - UU

Data Independence

• Logical Independence: The capacity to change the conceptual schema without having to change the external schema

oExample: Add another field to a conceptual schema

• Physical Independence: The capacity to change the internal schema without having to change the

conceptual schema

oExample: Put an access path(index) to reorganize the files

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2013-01-21 16 Silvia Stefanova, UDBL - IT - UU

Outline

1. Data Model, Database Schema

• Categories of data models

• Database schemas and instances

2. Data Independence

• Three-schema architecture

• Logical independence

• Physical independence

3. Database Languages

4. Classification of DBMS 5. To Summarize

(51)

2013-01-21 17 Silvia Stefanova, UDBL - IT - UU

Database Languages

• Database Language: Generic term for a class of

languages used for defining, communicating with or manipulating a database.

• Storage Definition Language (SDL) – to specify internal schema

• Data Definition Language (DDL) – to specify conceptual schema

• View Definition Language (VDL) – to specify user views

• Data Manipulation Language (DML) – to manipulate the data: insert, delete , update)

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2013-01-21 18 Silvia Stefanova, UDBL - IT - UU

Database Languages

• In the DDL the database administrator define the

internal and conceptual schema and in this manner the database is designed. Subsequent modifications in the schema design is also made in DDL.

• The DML used by DB users and application programs retrieve, add, remove, or alter the information in the database.

• SQL represents a combination of DDL, VDL and DML

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2013-01-21 19 Silvia Stefanova, UDBL - IT - UU

Outline

1. Data Model, Database Schema

• Categories of data models

• Database schemas and instances

2. Data Independence

• Three-schema architecture

• Logical independence

• Physical independence

3. Database Languages

4. Classification of DBMS 5. To Summarize

(54)

2013-01-21 20 Silvia Stefanova, UDBL - IT - UU

Classification of DBMS

• Criteria data model:

oRelational DBMS

oObject-oriented DBMS oObject-relational DBMS oGraph DBMS

• Criteria number of sites on which database is distributed

oCentralized DBMS oDistributed DBMS

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2013-01-21 21 Silvia Stefanova, UDBL - IT - UU

Classification of DBMS

• Criteria number of users:

oSingle-user DBMS oMulti-user DBMS

• Criteria purpose

oGeneral purpose DBMS oSpecial-purpose DBMS

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2013-01-21 22 Silvia Stefanova, UDBL - IT - UU

Outline

1. Data Model, Database Schema

• Categories of data models

• Database schemas and instances

2. Data Independence

• Three-schema architecture

• Logical independence

• Physical independence

3. Database Languages

4. Classification of DBMS 5. To Summarize

(57)

2013-01-21 23 Silvia Stefanova, UDBL - IT - UU

Summary

• Data model

• Database schema, database instance

• Data independence

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2013-01-21 24 Silvia Stefanova, UDBL - IT - UU

Components of a DBMS

(Figure 2.3 Elmasri/Navathe)

References

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