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Database System Concepts

and Architecture

Data Models

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A collection of concepts that can be used todescribe the structure of a database (data types,relationships, and constraints)

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basic operations (retrieval and updates)

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specify the dynamic aspect or behavior of adatabase application( user-defined operations )

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example: COMPUTE_GPA, which can be appliedto a STUDENT object

Conceptual Data Model

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Use concepts such as– Entities:a real-world object or concept (DEPT)

(COURSE)

• Attributes:property of interest that further describes an

entity (dept no, name, telephone, etc)

• Relationships:interaction among the entities (DEPT)

provides (COURSE)

Physical Data Model

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Describes how data is stored in the computer.

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It represents info such as– record formats– record orderings– access path: make search more efficient

Schemas

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Is the description of the database

not database itself

• Specified during database design–^

Not expected to change frequently

• A displayed schema is called a schema diagram (Fig 2.1) -^

Each object in the schema-such as STUDENT orCOURSE-is a schema construct.

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Schema diagram represents only some aspects of aschema (name of record type, data element andsome type of constraint)

The Three-Schema Architecture•^

Importance of using DB approach–

insulation of programs and data– support of multiple user views– use of a catalog to store the database description (schema).

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The aim is to separate the user application and physical DB

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schema can be defined into three levels:–

The internal level has an internal schema– describes the physical storage structure of the database.– uses a physical data model

Data Independence

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Is the capacity to change the schema at one level of adatabase system without having to change the schema atthe next higher level.

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Logical data independence: capacity to change theconceptual schema without having to change externalschemas or application programs.

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Physical data independence: capacity to change theinternal schema without having to change the conceptual(or external) schemas

DBMS Languages

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Data Definition Language DDL: Language to specifyconceptual and internal schemas for the database and anymappings between the two.

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Storage definition language SDL: used when cleardistinction between conceptual and internal schema.

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view definition language VDL: specify user views andtheir mappings to the conceptual schema.

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data manipulation language DML:retrieval, insertion,deletion, and modification of the data

DBMS Interfaces

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Menu-Based Interfaces for Browsing– menus leads to formulation of a request

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Forms-Based Interfaces– display a form for each user (insert, select)– designed for naïve users.

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Graphical User Interfaces (GUI)– display schema as diagram.– Utilize both menu and forms.

DBMS Interfaces

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Natural Language Interfaces– Accept requests in native language and attempt to

understand them.

• Refers to words in the schema and (standard words) to

interpret the request.

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Interfaces for Parametric Users (eg tellers)– goal is to min the number of keystroks required. (use of

function) keys

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Interfaces for the DBA– creating accounts, system privileges, changing schema,

etc.

• Jan 29,
• Jan 29,

Database System Utilities

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Loading: load existing files into the DB

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Backup: creates backup copy of the DB

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File reorganization: reorganize files for betterperformance

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Performance monitoring: monitor DB usage andprovide statistics to DBA