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What is database?
A very large collection of related data Models a real world enterprise:
Entities (e.g., teams, games / students, courses)
Relationships (e.g., The Celtics are playing in the Final!)
Even active components (e.g. “business logic”)
DBMS: A software package/system that can be used to store, manage and retrieve data form databases
Database System: DBMS+data (+ applications)
Why Study Database:
Shift from computation to information
Always true for corporate computing
More and more true in the scientific world and of course, Web
DBMS encompasses much of CS in a practical discipline
OS, languages, theory, AI, logic
Why not store everything on flat files: use the file system of the OS, cheap/simple…
Name, Course, Grade
John Smith, CS112, B
Jim Gray, CS560, A
John Smith, CS560, B+
Yes, but not scalable…
Data redundancy and inconsistency
Multiple file formats, duplication of information in different files
Name, Course, Email, Grade
John Smith, firstname.lastname@example.org, CS112, B
Mike Stonebraker, email@example.com, CS234, A Jim Gray, CS560, firstname.lastname@example.org, A
John Smith, CS560, email@example.com, B+
Why this a problem?
Potential inconsistencies (multiple formats, John Smith vs Smith J.)
Find the students who took CS560
Find the students with GPA > 3.5
For every query we need to write a program!
We need the retrieval to be:
Easy to write
No support for sharing:
Prevent simultaneous modifications
No coping mechanisms for system crashes
No means of Preventing Data Entry Errors
Database systems offer solutions to all the above problems.
A database is a collection of data elements (facts) stored in a computer in a systematic way, such that a computer program can consult it to answer questions. The answers to those questions become information that can be used to make decisions that may not be made with the data elements alone. The computer program used to manage and query a database is known as a database management system (DBMS). So a database is a collection of related data that we can use for
Ø Defining - specifying types of data
Ø Constructing - storing & populating
Ø Manipulating - querying, updating, reporting
A Database Management System (DBMS) is a software package to facilitate the creation and maintenance of a computerized database. A Database System (DBS) is a DBMS together with the data itself.
Features of a database:
Ø It is a persistent (stored) collection of related data.
Ø The data is input (stored) only once.
Ø The data is organized (in some fashion).
Ø The data is accessible and can be queried (effectively and efficiently).
• Collection of interrelated data
• Set of programs to access the data
• DMBS contains information about a particular enterprise
• DBMS provides an environment that it both convenient and efficient to use
Database management systems were developed to handle the following difficulties of typical file-processing systems supported by conventional operating systems:
• Data redundancy and inconsistency
• Difficulty in accessing data
• Data isolation –multiple files and formats
• Integrity problems
• Atomicity of updates
• Concurrent access by multiple users
• Security problems
Introduction to Databases
We live in an information age. By this we mean that, first, we accept the universal fact that information is required in practically all a used broadly here to mean any organisation of activities to achieve a stated purpose, including socio-economic activities. Second, we recognise further the importance of efficiently providing timely relevant information to an enterprise and of the importance of the proper use of technology to achieve that. Finally, we recognise that the unparallelled development in the technology to handle information has and will continue to change the way we work and live, ie. not only does the technology support existing enterprises but it changes them and makes possible new enterprises that would not have otherwise been viable.
The impact is perhaps most visible in business enterprises where there are strong elements of competition. This is especially so as businesses become more globalised. The ability to coordinate activities, for example, across national borders and time zones clearly depends on the timeliness and quality of information made available. More important perhaps, strategic decisions made by top management in response to perceived opportunities or threats will decide the future viability of an enterprise, one way or the other. In other words, in order to manage a business (or any) enterprise, future development must be properly estimated. Information is a vital ingredient in this regard.
Information must therefore be collected and analysed in order to make decisions. It is here that the proper use of technology will prove to be crucial to an enterprise. Up-to-date management techniques should include computers, since they are very powerful tools for processing large quantities of information. Collecting and analysing information using computers is facilitated by current Database Technology, a relatively mature technology which is the subject of this book.
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