Database Environment

1
Database Environment

• Chapter 2
• CIS548.101

2
The Three-Level ANSI-SPARC Architecture

• External
• Conceptual
• Internal
• ltfig. 2.1gt

3
Separation of Logical and Physical Presentation

• Each user should be able to access the same
  database, but have a different customized view of
  the data.
• Users should not have to deal directly with
  physical database storage details.
• DBA should be able to change the database storage
  structures without affecting the users views.
• The internal structure of the database should be
  unaffected by changes to the physical aspects of
  storage.
• The DBA should be able to change the conceptual
  structure of the database without affecting all
  users.

4
External Level

• Users view of the database. This level describes
  that part of the database that is relevant to
  each user.
• External views
• Different views may have different
  representations of the same data.

5
Conceptual Level

• The community view of the database. This level
  describes what data is stored in the database and
  the relationships among the data.
• Logical structure of entire database
• All entities, their attributes, and their
  relationships
• The constraints on the data
• Semantic information about the data
• Security and integrity information

6
Internal Level

• The physical representation of the database on
  the computer. This level describes how the data
  is stored in the database.
• Storage space allocation for data and indexes.
• Record descriptions for storage.
• Record placement
• Data compression and data encryption techniques.

7
Schemas

• Database schema
• External schemas (subschema)
• Different views of the data
• Conceptual schema
• Describes all the entities, attributes,and
  relationships together with integrity
  constraints.
• Internal schema
• Complete description of the internal model,
  containing the definitions of stored records, the
  methods of representation, the data fields, and
  the indexes and hashing schemes used.

8
(No Transcript)
9
Mappings

• The DBMS is responsible for mapping between these
  three types of schema.
• Check consistency.
• Conceptual/internal mapping
• Find the actual record of a logical record
• External/conceptual mapping
• Map names in the users view on to the relevant
  part of the conceptual schema

10
(No Transcript)
11
Database Instance

• Database schema is not expected to change
  frequently.
• Database instance
• The data in the database at any particular point
  in time.

12
Data Independence

• Upper levels are unaffected by changes to lower
  level.
• Logical data independence
• Refers to the immunity of the external schemas to
  changes in the conceptual schema.
• Physical data independence
• Refers to the immunity of the conceptual schema
  to changes in the internal schema.

13
Data Definition Language

• A language that allows the DBA or user to
  describe and name the entities, attributes,and
  relationships required for the application,
  together with any associated integrity and
  security constraints.
• System catalog (meta data, data dictionary)

14
Data Definition Language (DDL)

• The DDL is used to define a schema or to modify
  an existing one.
• System catalog
• Data dictionary

15
The Data Manipulation Language (DML)

• A language that provides a set of operations to
  support the basic data manipulation operations on
  the data held in the database.
• Insertion, modification, retrieval, deletion of
  data
• Query language
• Procedural DMLs
• Non-procedural DML (SQL)

16
Fourth-Generation Languages (4GLs)

• What v.s. How
• Forms generator
• Report generators
• Graphics generators
• Application generators

17
Data Models and Conceptual Modeling

• Data model
• An integrated collection of concepts for
  describing and manipulating data,relationships
  between data, and constraints on the data in a
  organization.
• Structural part
• Manipulation part
• Set of integrity rules
• Relational, network, hierarchical, Object-Oriented

18
Relational Data Model
19
Network Data Model
20
Hierarchical Data Model
21
Conceptual Modeling

• The process of constructing a model of the
  information use in an enterprise that is
  independent of implementations details such as
  the target DBMS, application programs,
  programming languages, or any other physical
  considerations.

22
Functions of a DBMS

• Data storage, retrieval, and update
• A user-accessible catalog (meta data)
• Transaction support (update salary)
• Concurrency control services
• Recovery service
• Authorization service
• Support for data communication

23
Functions of a DBMS (2)

• Integrity services
• Services to promote data independence
• Utility service
• Import, monitoring, statistical analysis, index
  reorganization, garbage collection.

24
Components of a DBMS

• Query processor
• Database manager
• File manager
• DML preprocessor
• DDL compiler
• Catalog manager
• Authorization control

25
Components of a DBMS (2)

• Command processor
• Integrity checker
• Query optimizer
• Transaction manager
• Scheduler
• Recovery manager
• Buffer manager

26
(No Transcript)
27
(No Transcript)
28
Multi-User DBMS Architectures

• Teleprocessing
• File-Server
• There is a large amount of network traffic
• A full copy of the DBMS is required on each
  workstation.
• Concurrency, recovery, and integrity control are
  more complex.
• Client-Server

29
(No Transcript)
30
Client-Server

• It enables wider access to existing databases.
• Increased performance.
• Different types of computers works in parallel.
• Hardware cost are reduced.
• Communication costs are reduced.
• Increased consistency single server
• It maps on to open-systems architecture naturally.

31
(No Transcript)