1 / 65

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

kira
Télécharger la présentation

MIS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

  21. Dr N Chaamwe

  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

  31. Dr N Chaamwe

  32. Dr N Chaamwe

  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

More Related