Presentation on theme: "Supplement 01 (a)Database-Introduction-1 Supplement 01a Database-Introduction-1 HSQ - DATABASES & SQL And Franchise Colleges By MANSHA NAWAZ."— Presentation transcript:
Supplement 01 (a)Database-Introduction-1 Supplement 01a Database-Introduction-1 HSQ - DATABASES & SQL And Franchise Colleges By MANSHA NAWAZ
Supplement 01 (a)Database-Introduction-1 Why Database Systems? Data is one of the most important resources in ALL organisations. Without data it is not possible to operate. Control manufacturing processes? Process sales of goods? Diagnose patients’ illnesses? Forecast sales? Run the University of Teesside? To be useful data must be processed into information. It must be: Accurate Timely Relevant Therefore, you need adequate facilities for storing data and processing information: –Storing (and verifying) data –Manipulating data –Extracting data
Supplement 01 (a)Database-Introduction-1 File - based approach Application Data Department Stock Control Production Accounts Part No, Supplier, qty location, reorder qty Stores Operations Finance Part#, qty, Assy#, Machine#, Cert.#: Supplier, Part#, Part#, Cost, Qty From the earliest days computers were used to store files of data. Separate systems, ie separate files and programs, were developed for each application, eg stock files, production files, accounts files, etc. Applications processed the data to provide information. Problems Inconsistency Redundancy Lack of integration Lack of control
Supplement 01 (a)Database-Introduction-1 Database approach Application Database Supplier, Supplier Pt No:, Part No: Cost, Qty ordered, Qty del., qty, Assy No:, Machine No:, Cert. No: location, reorder qty Database Management System DBMS Stock Control Production Accounts Department DBMS is the environment used to manage a database The database consisting of stored data and processed information for a system Data are organised into a single set of underlying TABLES from which the applications draw the data to provide information that are relevant to them.
Supplement 01 (a)Database-Introduction-1 E-R Model NF Systems Analysis & Design DFD DataStores, DataFlows and Data Dictionary DBMS PHYSICAL VIEW OF DATA TABLES LOGICAL VIEW OF DATA FORMS DATA MODEL TABLE SET Database connectivity via websites technology Macromedia Dreamweaver MS Visual Studio Database connectivity via desktop DBMS such as MS Access Database connectivity via programming languages such as MS Visual Basic Area of Interest Database Development
Supplement 01 (a)Database-Introduction-1 Client/Server Architecture User Workstation Operator Workstation Department File-Servers Corporate Servers Server provides services for the Clients which are responsible for interacting with the users (Input/Output) Server is responsible for performing a service (e.g. transaction) and guaranteeing the integrity of the data Well suited for distributed systems handling large amounts of data
Supplement 01 (a)Database-Introduction-1 System Development Overview Systems development undertaken by using Case Tools –used early in development life cycle –Provide requirements and design in terms of Systems Model and Data Model Case Tools for Systems Modelling: –Dataflow Diagrams (DFD) –Data Dictionary (DD) Case Tools for Data Modelling: –Normalisation (NF)Normalisation (NF) –A rules based technique undertaken to produce the data model for a system –Entity Relationship Model (ER) –A diagrammatic based technique undertaken to produce the data model for a system –DFD & DD provide us with the base for a ERD Data Model Data Model –Can be implemented on a DBMS such as MS SQL Server, MS Access, etc –Consists of logical and physical view of the proposed systems data. DBMS – implementation platform –Database Management System such as MS SQL Server 2000 (MS Access)
Supplement 01 (a)Database-Introduction-1 MS SQL Server is a server based database. Multi User – Multi Platform Systems Large, high volume traffic database systems Server holds database. Workstation provides access. For web or database systems if the access traffic is likely to generate more than 20 concurrent database hits at a time, it's time to move to a database server Generally, database servers like MS SQL Server are the way to go for database or web/database systems Many and wide ranging user base for system Additional Security and Login features MySQL (free sql database used for connectivity to Websites via PHP). MS SQL Server V MS Access MS Access is Desktop based Small, low-traffic database systems Small, low-traffic web sites requiring database connectivity. Cannot handle heavy traffic from multiple users.
Supplement 01 (a)Database-Introduction-1 Advantages of the Database Approach No unnecessary duplication of data. Greater consistency of data. Wider availability of data. Greater flexibility of use of data. Improved data integrity. Improved security. Improved backup and recovery services. Can change the data structure without altering associated programs. A database is dynamic: it can grow and change. Data management can be more consistent and systematic.
Supplement 01 (a)Database-Introduction-1 Databases “A shared collection of logically related data, and a description of this data, designed to meet the information needs of an organisation.” ‘Database Systems’ by Connolly & Begg Addison-Wesley, ISBN “A database system can be thought of as a computerised record-keeping system. Such a system involves the data itself (stored in the database), hardware, software and – most important! – users. … Databases are integrated and (usually) shared; they are used to store persistent data.” ‘An Introduction to Database Systems’ by C J Date, Addison-Wesley, ISBN (7th Edition, 2000)
Supplement 01 (a)Database-Introduction-1 DBMS “A software system that enables users to define, create, maintain, and control access to the database.” Provides the interface between the user and the data in the database. Allocates storage to data and maintains indices so that any required data can be retrieved. Protects data against unauthorised access. Safeguards data against corruption. Provides recovery and restart facilities after a hardware or software failure.
Supplement 01 (a)Database-Introduction-1 Also referred to as Conceptual Model –A Data Model provides a particular way of thinking about data, at least in terms of its structure –Data Models include data descriptions, data relationships, data semantics, consistency constraints [Silberschatz et. al.] –Data model comprises three components: data structures, data manipulators, and general integrity rules [Codd (1970)] A Data Model is implementation independent –Not aimed at any particular computer software or hardware. DBMS supports an implementation of one or more Data Models –What data model is supported by a Relational Database Management System (Access, SQL, Oracle, etc.) –A RDBMS may have extensions to support other models. At what stage in the Systems Development Lifecycle will data modelling take place (early, middle, late)? Data Model
Supplement 01 (a)Database-Introduction-1 –Data Models produced early in Systems Development –Makes improvements in terms of : NO DUPLICATION or REDUNDANT or NULL INFORMATION REDUCTION IN PHYSICAL SIZE QUICKER INFORMATION RETRIVAL LEADS TO A FULLY OPTIMISED SET OF TABLES –Data Model produced by Case Tools techniques Normalisation –Rule based technique for transfering logical datastore view to physical view Entity Relationship Modelling. –Diagrammatic representation of a proposed systems database requirements –Data Model provides a full set of related tables and data Able to derive physical views (internal schema) of data Able to derive logical views (external schema) of data Data Model
Supplement 01 (a)Database-Introduction-1 Provide us with a Bottom Up approach to producing the database tables Technique covered in other modules Supplement on Normalisation is provided on the DD website Normalisation (NF) Entity Relationship Modelling (ERM) A data modelling CASE Tool Technique of interest A diagrammatic representation of a systems database tables Top Down approach to data modelling Entity Relationship Diagram (ERD) used to map data model Applying rules, translate ERD into a set of well-normalised tables Provides both logical and physical view of tables
Supplement 01 (a)Database-Introduction-1 –TABLES –DATA –Internal Schema View –database structure view that a DBMS requires. –in terms of Tables, Attributes (data fields) and Types (data defn.) –linkage between tables via primary and foreign keys –All Datastores decomposed to a set of TABLES –Physical View – for Designers PHYSICAL VIEW –FORMS –INFORMATION –External Schema View –Form or Screen views provided to the end user. –A set of FORMS derived from the TABLES –Logical View – for Users LOGICAL VIEW
Supplement 01 (a)Database-Introduction-1 The Three Level ANSI-SPARC Architecture In 1975 the ANSI Standards Planning and Requirements Committee proposed a standard terminology and general architecture for database systems. The objective is to separate each user’s view of the database from the way it is physically represented. 3 levels or views of data within a database: External Level –The users’ view of the database. Also known as the applications view. Conceptual Level –The overall view of the database. Also known as the global view. Internal Level –The physical representation of the database on the computer. Also known as the storage view.
Supplement 01 (a)Database-Introduction-1 Schemas The overall description of the database is called the database schema. There are 3 different types of schema in the database. External Schema –There are multiple external schemas (or subschemas), each one corresponding to a different view of the data. Conceptual Schema –There is one conceptual schema, which describes the data stored in the database, the relationships and the integrity constraints. Internal Schema –There is one internal schema, which describes how the data are stored in the database and how they are accessed.
Supplement 01 (a)Database-Introduction-1 Schemas and Views Inventory H R Finance Production Customer Service Conceptual Internal External
Supplement 01 (a)Database-Introduction-1 Mapping Provides the translation between the schemas at different levels. The DBMS is responsible for mapping between the 3 types of schema. The DBMS must ensure that each external schema is derivable from the conceptual schema. The DBMS must use the information in the conceptual schema to map between each external schema and the internal schema.
Supplement 01 (a)Database-Introduction-1 Data Independence A major objective for the 3-level architecture is to provide data independence, ie upper levels must be unaffected by changes to lower levels. There are 2 kinds of data independence: Logical data independence –refers to the immunity of the external schemas to changes in the conceptual schema. –It should be possible to alter tables, columns or relationships without having to alter existing external schemas or rewrite application programs (other than those that are directly affected). Physical data independence –refers to the immunity of the conceptual schema to changes in the internal schema. –It should be possible to alter file organizations, storage devices, indexes, etc, without having to alter the conceptual or external schemas.
Supplement 01 (a)Database-Introduction-1 The Systems Catalogue The database schema is defined using a special language called a Data Definition Language (DDL). The result of the compilation of the DDL statements is a set of tables stored in special files collectively called the system catalog. This is a repository of meta-data (data about data), ie information describing the data in the database, typically containing the name, description, source and usage information for each data item. The system catalog is also known as the data dictionary or the data directory.
Supplement 01 (a)Database-Introduction-1 Database Language A Data Definition Language (DDL) is used to specify the data in the database. A Data Manipulation Language (DML) is used to access the data. A Data Control Language (DCL) is used to control access to the data. Some databases have a combined DDL, DML and DCL (often called a Query Language), eg SQL.
Supplement 01 (a)Database-Introduction-1 Database Types - 3 Main Data Models Each database uses a definition language –imposes restrictions on what can be defined how entities relate to each other Network model Hierarchical model Relational model
Supplement 01 (a)Database-Introduction-1 Database Types - Network Part No: Supplier Name Supplier Part No: Link File Can show all 1:n relationships between records
Supplement 01 (a)Database-Introduction-1 Database Types - Hierarchical Supplier Part No:Supplier Code Location ElectricalSteelOilsFasteners Quantity Supplier Name STOCK Part No:
Supplement 01 (a)Database-Introduction-1 Data Files STOCK ITEM RECORD STOCK ITEM FILE FIELD(S) Part No: Colour Weight Description Quantity Reorder Qty Location Supplier Name Supplier Code Supplier Part No: N/A 98 F37 Cadmium Bar 90mm dia 7 4 Ferris F2 c FIELD VALUES KEY FIELD PRIMARY KEY Database Types - Relational
Supplement 01 (a)Database-Introduction-1 Logical vs. Physical STOCK ITEM FIELD(S) Part No: Colour Weight Description Quantity Reorder Qty Location Supplier Name Supplier Code Supplier Part No: N/A 98 F37 Cadmium Bar 90mm dia 7 4 Ferris F2 c FIELD VALUES LOGICAL PHYSICAL Database Types - Relational
Supplement 01 (a)Database-Introduction-1 Relationships - 1:1 STOCK ITEM Part No: Colour Weight Description Quantity Reorder Qty Location Supplier Code N/A 98 F37 Cadmium Bar 90mm dia 7 4 Ferris F2 c Supplier Name Supplier Part No:
Supplement 01 (a)Database-Introduction-1 Relationships - 1:n STOCK ITEM Part No: Colour Weight Description Quantity Reorder Qty Location Supplier Name Supplier Code N/A 98 F37 Cadmium Bar 90mm dia 7 4 Ferris F2 c Supplier Part No:
Supplement 01 (a)Database-Introduction-1 Relationships - m:n STOCK ITEM Part No: Colour Weight Description Quantity Reorder Qty Location Supplier Name Supplier Code N/A 98 F37 Cadmium Bar 90mm dia 7 4 Ferris F2 c Supplier Part No:
Supplement 01 (a)Database-Introduction-1 Relational Model Technique Future Lectures will cover the Entity Relationship Diagrams (ERD’s)