Module 2: Database Environment

Overview Three –Level ANSI-SPARC Architecture Database language Data Models and Conceptual Modeling Function of DBMS Components of DBMS Multi user DBMS Architecture Data Dictionary

Three –Level ANSI-SPARC Architecture External Level The users view of database.---Relevant to the particular user Conceptual Level The community view of the database. ----what data is stored in database, and relationships Internal Level The physical representation of the database on the computer---How data is stored in database.

Three –Level ANSI-SPARC Architecture User1 User2 User n View1 View2 View n External Level Conceptual Level Conceptual Schema Internal Schema Internal Level Physical Data Organization Database

Database Languages A data sublanguage consists of two parts DDL A Descriptive language that allows the DBA or user to describe and name of entities required for the application and relationships that may exists between the different entities DML A language that provides a set of operations that support the basic data manipulation operations on the data held in the database.

Database Languages DML Insertion Update (Modification) Retrieval (Selection) Deletion

Database Languages Types of DML Procedural A language that allows the user to tell the system exactly how to manipulate the data. Treats records individually Non Procedural A language that allows the user to state what data is needed rather than how it is to be retrieved. Statements operate sets of records

Data Models and Conceptual Modeling An integrated collection of concepts for describing data, relationships between data and constraints on the data in an organization. Object Based Data Models Record Base Data Models Physical Data Models Conceptual Data Models

Object Based Data Models This model use the concepts such as entities, attributes and relationships. Entities (Person, Place or thing, concept or event) Attributes (Properties) Relationships (association between entities)

Record Base Data Models Database consists of number of fixed-format records of possibly different types , each record define number of different fields and each typically fixed length. Relation Data Model Network Data Model Hierarchical Data Model

Relation Data Model The relational data model is the based on the concept of mathematical relation DeptId Depart Name 1 Accounts 2 H.R 3 MIS Empid Name Age Deptid 1 Ali 34 2 Ahmad 30 3 Bilal 40 4 Waseem

Network data Model In the network model, data is represented as collection of records and relationships are represented by sets.

Hierarchical data modal The hierarchal modal is a restricted type of network model .again data is represented as collection of records and relationship are represented by sets

Physical data model Physical data model is describe how save data in computer, representing information such as record structures ,record ordering and access path .

Conceptual modeling We can see that the conceptual schema is the heart of the database. It supports all the external views and is, in turn, supported by the schema.

Functions of DBMS Data storage, retrieval and update A DBMS must furnish users with the ability to store, retrieve and update data in the database. A user accessible catalog A DBMS must furnish a catalog in which descriptions of data items are stored and which is accessible to users

Functions of DBMS Transaction Support A DBMS must furnish a mechanism which will ensure that either all the Updates corresponding to a give transaction are made or that none of them are made Concurrency control services A DBMS is must furnish a mechanism to that the database is updated correctly when multiple users are updating the database concurrently.

Functions of DBMS Recovery services A DBMS must furnish a mechanism for recovering the database in the event that the database is damaged in any way. Authorization services A DBMS must furnish a mechanism to ensure that only authorized users can access the database Support for Data Communication A DBMS must be capable of integrating with communication software.

Functions of DBMS Integrity Services A DBMS must furnish a means to the both the data in the database and changes in the data flow certain rules. Services to data independence A DBMS must include facilities to support independence of programs from the structure of the database. Utility Services A DBMS should provide a set of utility services

Multiple –user DBMS architectures Teleprocessing File-server Clint-server

Data Dictionaries Data Dictionary: a repository of information description the database that is the metadate or the data about the data The names of users authoresses to use DBMS; The names of the data items in the database ; The data items that each use can access and the type of allowed for example, insert, update, or read access.