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

Introduction to Databases Dr N Chaamwe

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

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

File-based Processing Dr N Chaamwe

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

File structure is defined in the program code. 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

Database Approach Arose because: Result 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

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

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

Database Management System (DBMS) Dr N Chaamwe

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

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

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

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

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

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

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

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

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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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

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

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

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

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

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

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

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

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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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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Lifecycle of Database system development

Lifecycle of Database system development Dr N Chaamwe

Lifecycle of Database system development Dr N Chaamwe

Lifecycle of Database system development Dr N Chaamwe

Planning phase Prior to the first phase of our requirement’s elicitation, a plan must be put forward showing each stage of the life cycle and how it can be performed efficiently and effectively. Dr N Chaamwe

System definition phase, This is where the scope and boundaries of the database application, which includes the major application areas and user groups, are defined. Dr N Chaamwe

Requirement collection and analysis Phase It is concerned with collecting the data and analyzing the user requirements in order to build the database application. Dr N Chaamwe

Conceptual model. Create a conceptual schema (High-Level), e..g. ERD Dr N Chaamwe

Logical Design Map conceptual database schema to logical database schema (Representational), it is also called an Implementation model e.g. Relational Dr N Chaamwe

Physical Design Internal storage structures and file organisations are specified (Physical), e.g. B-tree Dr N Chaamwe

The prototype This is a working model of the database application, which allows the designers or users to visualize and evaluate how the final system will look and function. Dr N Chaamwe

Implementation The phase involves the creation of the external, conceptual and internal definitions and the application programs. Dr N Chaamwe

Data Conversion and Loading If we have a legacy system at this stage, then we need to transfer any existing data into the new database and converting any existing application. Dr N Chaamwe

The testing phase Validating user requirements against the application programs then tests the system. The testing phase aims at executing the application programs with intention to find errors Dr N Chaamwe

Operational maintenance This process involves monitoring & maintaining the system. Dr N Chaamwe