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Transcript of 1 Database Management Systems (DBMS). 2 Database Management Systems (DBMS) n Overview of: ä...
1
Database Management Systems
(DBMS)
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Database Management Systems (DBMS)
Overview of:
Database Management Components
Database Systems Architecture (DSA)
DBMS Functions The Database Approach
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Database Management Overview
A database system is comprised of four major components:
Data, Hardware, Software and Users. Data in a database is both:
Integrated– The database is a unification of several files,
with redundancy eliminated. Shared
– Individual pieces of data can be shared amongst different users. Different users can access the data at the same time (concurrent access).
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Main Advantages of a DBMS
scalability – Expanded, Modified or downsized
Support for client/server systems
Economy of Scale- better utilization of hardware.
Sharing of data
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Main Advantages of a DBMS Balancing Conflicting
requirements.-typically a DBMS is managed by a person called a database administrator(DBA)
Controlled Redundancy Security-The DBA can define
authorization procedures to ensure only legitimate users can access the database.
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DBMS
DBMS require more expensive Hardware Software Data networks capable of
supporting a multi-user environment
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DBMS
DBMS is more complex than a file processing system. Learning curve for systems
analysts, database administrators and users is usually steeper
This increase total cost of ownership (TCO)
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DBMS Components
Provides an interface between a database and the users
Data manipulation language a schema and a physical data repository
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DATABASE
Data manipulation language
Schema and subschema's
Physical data repository
Users
Database
Administrators
Related
Information
Systems
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Users
Users. Users typically work with predefined queries, forms, reports and switchboards, but can also use query languages to access stored data.
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Data Manipulation Language
Controls database operations Storing Retrieving Updating Deleting data
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Data Manipulation Language
Commercial DBMS Oracle and IBM’S DB/2
Use a DML
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Schema
The complete definition of a database including descriptions of all fields, records and relationships.
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Database System Architecture
Three Levels of the ANSI/SPARC architecture:
Internal (Physical) Low level representation of the database,
i.e. indexes. External (User Logical)
The individual user level Conceptual (Community logical)
A view of the total database contents, definitions, security, integrity constraints
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DBMS
The DBMS handles all access to the database. User issues an access request. DBMS intercepts request and
analyses it. DBMS inspects, the external schema
for the user, the conceptual scheme and storage structure definition.
DBMS executes the operations on the stored database.
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DBMS Functions:
Data Definition (DDL compiler or processor) Data Manipulation (DML compiler or
processor) Optimisation and Execution (run-time
manager) Data Security and Integrity Data Recovery and Concurrency (transaction
manager) Data Dictionary (metadata) Performance
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Client/Server Architecture
In this context the DBMS is the server as it supports all the basic functions, data definition, data manipulation, data security and integrity.
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Client/Server Architecture
Clients: the applications that run on top of the DBMS.
Applications
DBMS
End users
Clients
Server
Database
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Distributed Database System
When a system provides total transparency, i.e. each client behaves as if it was dealing with a single server on a single machine = distributed database system.
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The Database Approach:Advantages
Centralised Control Standardisation Balancing Visibility Integrated Processing Controlled redundancy of data Data independence
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The Database Approach:Disadvantages
Cost of Initial Conversion Purchase Installation Training New applications Data entry
Operating Costs – DBMS are resource hungry.
Success – performance degradation Politics (naming conventions)