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MIS

MIS. CA – 40% Assignment Test Exam – 60% Lecture slides www.chaamwe.weebly.com Taught Courses. Int roduction to Databases. Database systems vs. file-based systems. Examples of DBSs: Purchases from the supermarket Purchases using your credit card Booking a holiday at the travel agents

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MIS

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  1. MIS • CA – 40% • Assignment • Test • Exam – 60% • Lecture slides • www.chaamwe.weebly.com • Taught Courses Dr N Chaamwe

  2. Introduction to Databases Dr N Chaamwe

  3. Database systems vs. file-based systems • Examples of DBSs: • Purchases from the supermarket • Purchases using your credit card • Booking a holiday at the travel agents • Using the local library • Taking out insurance • Using the Internet • Studying at university Dr N Chaamwe

  4. File-based Systems • Collection of application programs that perform • services for the end users (e.g. reports). • Each program defines and manages its own data. Dr N Chaamwe

  5. File-based Processing Dr N Chaamwe

  6. Limitations of File-based Approach • Separation and isolation of data • Each program maintains its own set of data. • Users of one program may be unaware of potentially useful data held by other programs. • Duplication of data • Same data is held by different programs. • Wasted space and potentially different values and/or different formats for the same item Dr N Chaamwe

  7. Data dependence • File structure is defined in the program code. • Incompatible file formats • Programs are written in different languages, and so cannot easily access each others files. • Fixed Queries/Proliferation of application programs • Programs are written to satisfy particular functions. • Any new requirement needs a new program. Dr N Chaamwe

  8. Database Approach • Arose because: • Definition of data was embedded in application programs, rather than being stored separately and independently. • No control over access and manipulation of data beyond that imposed by application programs. • Result • the database and Database Management System (DBMS). Dr N Chaamwe

  9. Database various definitions • DB: • Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization. • System catalog (metadata) provides description of data to enable program–data independence. • Logically related data comprises entities, attributes, and relationships of an organization's information. Dr N Chaamwe

  10. DBMS: • A software system that enables users to define, create, and maintain the database and which provides controlled access to this database. Dr N Chaamwe

  11. Database Management System (DBMS) Dr N Chaamwe

  12. Database languages • Data definition language (DDL). • Permits specification of data types, structures and any data constraints. All specifications are stored in the database. • Provides basic data manipulation operations on data held in the database. Dr N Chaamwe

  13. Database languages • Data manipulation language (DML). • General enquiry facility (query language) of the data. • Procedural DML • allows user to tell system exactly how to manipulate data. • Non-Procedural DML • allows user to state what data is needed rather than how it is to be retrieved. Dr N Chaamwe

  14. Database languages • Data Control language (DCL). • General administration & security facility (same syntax as query language) used mainly by the DBA. Dr N Chaamwe

  15. Views • A view mechanism. • Provides users with only the data they want or need to use. • Allows each user to have his or her own view of the database. • A view is essentially some subset of the database. Dr N Chaamwe

  16. Views Benefits include: • Reduce complexity; • Provide a level of security; • Provide a mechanism to customize the appearance of the database; • Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed Dr N Chaamwe

  17. Three-level schema architecture • ANSI-SPARC architecture is named after the committee that proposed it, the American National Standard Institute, Standards Planning And Requirements Committee. Dr N Chaamwe

  18. Objectives of Three-Level Architecture • All users should be able to access same data. • A user's view is immune to changes made in other views. • Users should not need to know physical database storage details. Dr N Chaamwe

  19. Objectives of Three-Level Architecture • DBA should be able to change database storage structures without affecting the users' views. • Internal structure of database should be unaffected by changes to physical aspects of storage. Dr N Chaamwe

  20. Objectives of Three-Level Architecture • DBA should be able to change conceptual structure of database without affecting all users. Dr N Chaamwe

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  22. The External level • The external level (also known as the user logical level) is the one closest to the users. • It is the level concerned with the way the data is seen by individual users. Dr N Chaamwe

  23. The External level • The external schema is used to describe the external level. • It contains a description of a portion of the database that is of concern to the specific user. Dr N Chaamwe

  24. The External level • The external view is described in terms of external records, which may be different form the actual stored records. • The view may have a different representation of the same data Dr N Chaamwe

  25. The Conceptual level • The level represents the community view of the database as seen by the database administrator. • It is also known as the community logical level or even sometimes just the logical level. Dr N Chaamwe

  26. The Conceptual level • The conceptual schema is used to describe what data is stored in the database and the relationships among the data. • The description includes the structure and constraints for the whole database Dr N Chaamwe

  27. The Conceptual level • the conceptual schema defines the logical structure of all data in the database. • The conceptual schema is defined by a Data Definition Language (DDL). • There is only one conceptual schema for the database. Dr N Chaamwe

  28. The Internal level • It is the description of the implementation of the conceptual schema by means of physical storage structures. • It summarizes how the data are stored on secondary storage devices such as disks and tapes. Dr N Chaamwe

  29. The Internal level • However, it is still one level above the actual physical storage, which is usually managed by the operating system. • The internal level does not deal with the physical records but it deals with the internal records (stored records). Dr N Chaamwe

  30. The Internal level • Details of how the address space is mapped to physical storage are highly system-specific (e.g. a block or a page) Dr N Chaamwe

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  33. Logical Data Independence –Refers to immunity of external schemas to changes in conceptual schema. – Conceptual schema changes (e.g. addition/removal of entities). – Should not require changes to external schema or rewrites of application programs. Dr N Chaamwe

  34. Physical Data Independence – Refers to immunity of conceptual schema to changes in the internal schema. – Internal schema changes (e.g. using different file organizations, storage structures/devices). – Should not require change to conceptual or external schemas. Dr N Chaamwe

  35. Data Independence • Describes the immunity of the upper levels from the changes in the lower levels Dr N Chaamwe

  36. Mappings • The process of transforming requests and results between levels are called mappings. • The three-level architecture involves certain mappings— one conceptual/internal mapping and several external/conceptual mappings. Dr N Chaamwe

  37. The conceptual/internal mapping • defines the correspondence between the conceptual view and the stored databases • If a change is made to the storage definition, then the conceptual/internal mapping must be changed accordingly, so that the conceptual schema can remain invariant Dr N Chaamwe

  38. The external/conceptual mapping • defines the correspondence between a particular external view and the conceptual view. • If a change is made to the conceptual schema definition, then the External/conceptual mapping must be changed accordingly, so that the External Schema can remain invariant Dr N Chaamwe

  39. Functions of a DBMS • Data Storage, Retrieval, and Update. • A User-Accessible Catalog. • Transaction Support. • Concurrency Control Services. • Recovery Services. Dr N Chaamwe

  40. Functions of a DBMS • Authorization Services. • Support for Data Communication. • Integrity Services. • Services to Promote Data Independence. • Utility Services. Dr N Chaamwe

  41. Roles in the Database Environment • Data Administrator (DA) • Database Administrator (DBA) • Database Designers (Logical and Physical) • Application Programmers End Users (naive and sophisticated) Dr N Chaamwe

  42. Advantages of DBMS • Control of data redundancy • Data consistency • More information from the same amount of data. • Sharing of data Dr N Chaamwe

  43. Advantages of DBMS • Improved data integrity • Improved security • Enforcement of standards • Economy of scale • Improved data accessibility and responsiveness Dr N Chaamwe

  44. Advantages of DBMS • Balanced conflicting requirements • Increased productivity • Improved maintenance through data independence • Increased concurrency • Improved backup and recovery services Dr N Chaamwe

  45. Disadvantages of DBMS • Complexity • Size • Cost of DBMS • Additional hardware costs • Cost of conversion • Performance • Higher impact of a failure Dr N Chaamwe

  46. When a DBMS may be unnecessary • If the database and applications are simple, well defined, and not expected to change • If there are stringent real-time requirements that may not be met because of DBMS overhead. • If access to data by multiple users is not required. Dr N Chaamwe

  47. Information Resource Dictionary System (IRDS) • Also called as a Data Dictionary or System Catalog • A repository of information (meta-data) describing the data in the database. Dr N Chaamwe

  48. Information Resource Dictionary System (IRDS) • It is a tool which enables one to control and manage the information about the data in the design, implementation and expansion phases of a DB Dr N Chaamwe

  49. Information Resource Dictionary System (IRDS) • Typically stores: • Names of authorized users. • It is used by modules such as: • Authorization Control. • Integrity Checker. Dr N Chaamwe

  50. Information Resource Dictionary System (IRDS) • Who benefits from the use of DDS? • DB administrators • Data administrators • Application personnel • Operating staff • End users • Data auditors. Dr N Chaamwe

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