File Processing - Database Overview MVNC1 DATABASE SYSTEMS Overview.

File Processing - Database Overview MVNC 1

DATABASE SYSTEMS

Overview


DATABASE SYSTEMS

A database may be defined as a collection of interrelated data stored together without harmful or unnecessary redundancy to serve multiple applications» the data are stored so that they are independent of

programs which use the data

» a common and controlled approach is used in adding new data and in modifying and retrieving existing data within the data base.

» The data is structured so as to provide a foundation for future application development.


DATABASE SYSTEMS

Components

App. 1

App. 2

App. 3

App. 4

Databasesystem

Database

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Teachers

ClassesPayroll


DATABASE SYSTEMS

Important considerations» Sharing» Data Integraty» Redundancy» Growth» Logical data independence» Physical data independence


DATABASE SYSTEMS

Redundancy» A database should minimize redundancy.

– controlled or minimal redundancy for capability to recover from loss some redundancy may exist in order to give improved

access time or simpler address methods

– harmful redundancy cost of storing multiple copies necessary to update multiple copies system may be inconsistent when in different stages of

updating


DATABASE SYSTEMS

Constant Growth - a data base is not a static entity» to allow for change over time, with possible

restructuring of the physical data.» new data and applications may be added» data independence


DATABASE SYSTEMS

Logical data independence» the overall logical structure of the data may be

changed without changing the application programs.

» The changes must not, of course, remove any of the data the application programs use.)


DATABASE SYSTEMS

Physical data independence» the physical layout and organization of the data

may be changed without changing either the overall logical structure of the data or the application programs.


DATABASE SYSTEMS

Data Views» External View

– View of data from a partiular program.– Multiple views may exist for multiple needs

» Conceptual View– Complete discription of data stored

» Internal View– Physical organization of actual data


DATABASE SYSTEMS

Conceptual View» While the programmer's view of data change and

the physical storage and organization change, the conceptual model remains stable or grows to incorporate more data types.

» Describes the entire set fields and relationships in the data

» Called the schema


DATABASE SYSTEMS

Conceptual View» The Schema is the underlying view of the data,

from which all external views can be derived» A well designed conceptual model will only need to

grow, a badly designed model will have to be modified and changed later.


DATABASE SYSTEMS

External View» Each use of the data may require a different

external view» Permits access to subsets of the data

– Security - some data is hidden, readonly– Flexibility - schema changes shouldn't affect programs– Understanding - programers and users need not

understand the complexities of the underlying data


DATABASE SYSTEMS

Internal View» Only the database management system need

know this» indexes, file structures, access techniques, etc.» DB administrator may modify parameters for

performance.


DATABASE SYSTEMS

The Objectives of a Data-Base organization» The ultimate objective is to make application

development easier, cheaper, faster, and more flexible.

» A data-base should be a repository of the data needed for an organization data processing.

» The conceptual view should reflect the "true properties of the data."


DATABASE SYSTEMS

Primary Objectives of Data-Base Organization» The Data Base is the Foundation Stone of Future

Application Development– It should make application development easier, cheaper, faster

and more flexible.

» The Data Can Have Multiple Uses– Different users who perceive the same data differently can

employ them in different ways.

» Intellectual Investment is Protected– Existing programs and logical data structures (representing

many man-years) will not have to be redone when changes are made to the data base.


DATABASE SYSTEMS

Primary Objectives of Data-Base Organization» Clarity

– Users can easily know and understand what data are available to them.

» Ease of Use– Users can gain access to data in a simple fashion.– Complexity is hidden from the users by the data-base

management system.

» Flexible Usage– The data can be used or searched in flexible ways with

different access paths.


DATABASE SYSTEMS

Primary Objectives of Data-Base Organization» Unanticipated Requests for Data Can Be Handled Quickly

– Spontaneous requests for data can be handled without application programs having to be written (a time-consuming bottleneck), by means of high-level query or report generation languages.

» Change Is Easy– The data base can grow and change without interferring with

established ways of using the data.

» Low Cost– Low cost of storing and using data, and minimization of the high

cost of making changes.


DATABASE SYSTEMS

Primary Objectives of Data-Base Organization» Less Data Proliferation

– New application needs may be met with existing data rather creating new files.

» Performance– Data request can be satisfied with speed suitable to the

usage of the data.

» Accuracy and Consistency– Accuracy controls will be used.

– The system will avoid having multiple versions of the same data item available to users in different stages of updating.


DATABASE SYSTEMS

Primary Objectives of Data-Base Organization» Protection from Loss or Damage» Privacy

– Unauthorized access to the data will be prevented.– The same data may be restricted in different ways from

different uses.– Data will be protected from failures and catastrophes, and

from criminals, vandals, incompetents, and persons who might falsely update them.

» Availability – Data are quickly available to users at almost all times when

they need them.


DATABASE SYSTEMS

Secondary Objectives (to help achieve the primary objectives)» Physical Data Independence

– Storage hardware and physical storage techniques can be changed without causing application program rewriting.

» Logical Data Independence– New data items can be added, or the overall logical structures

expanded, without existing programs having to be rewritten.

» Controlled Redundancy– Data items will be stored only once except where there are

technical or economic reasons for redundant storage.


DATABASE SYSTEMS

Secondary Objectives» Suitably Fast Access

– Access mechanisms and addressing methods will be fast enough for the usage in question.

» Suitably Fast Searching– The need for fast spontaneous searching of the data will grow

as interactive systems usage spreads.

» Data Standardization Within a Corporation– Interdepartmental agreement is needed on data formats and

definitions.– Standardization is needed between departments who would

otherwise have created incompatible data.


DATABASE SYSTEMS

Secondary Objectives» Data Dictionary

– A data dictionary, defining all data items used, is needed.

» High-level Programmer Interface– Application programmers should use simple, powerful

data requests and be insulated from the complexities of file layout and addressing.

» End User Language– A high-level query or report-generation language should

permit some end users to bypass the application programming step.


DATABASE SYSTEMS

Secondary Objectives» Integrity Controls

– Range checks and other controls should detect data inaccuracies where possible.

» Fast Recovery from Failures– Automatic recovery without loss of transactions.

» Tunability– The data base should be tunable, to improve

performance without causing application program rewriting.


DATABASE SYSTEMS

Secondary Objectives» Design and Monitoring Aids

– Aids which permit the designer of data administrator to predict and optimize performance.

» Automatic Reorganization or Migration– Data migration or other automatic physical reorganization

designed to improve performance.

» Evolution to Distributed Data Base Operation– The system should be designed so that distributed

processing and computer network operations can evolve.

File Processing - Database Overview MVNC1 DATABASE SYSTEMS Overview.

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