Download DBMS Architecture And Design and more Lecture notes Deductive Database Systems in PDF only on Docsity!
DATABASE SYSTEMS
COMSATS University, Islamabad
Abbottabad Campus
Computer Science Department
Mukhtiar Zamin, MS (Computer Science) Iowa, United States of America [email protected] Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models 1
Lecture 3
- (^) DBMS Architecture
- (^) The Three-Level ANSI-SPARC Architecture
- (^) External Level
- (^) Conceptual Level
- (^) Internal Level
- (^) Physical Data Organization
- (^) Differences between Three Levels of ANSI-SPARC Architecture
- (^) Objectives of Three-Level Architecture
- (^) Database Schema
- (^) Data Independence
- (^) Database Languages
- (^) Data Models and Conceptual Modeling
- (^) Object Based Data Model
- (^) Record-based Data Models
- Physical Data Models
- (^) Conceptual Modeling Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models 2
The Three-Level ANSI-SPARC Architecture
- (^) The American National Standards Institute (ANSI) Standards Planning
and Requirements Committee (SPARC) produced this architecture in
1975 (ANSI, 1975).
- (^) It comprising an external, a conceptual and an internal level
- (^) External level: The way users perceive the data
- (^) Internal level: The way the DBMS and the operating system perceive the data , where the data is actually stored using the data structures and file
- (^) Conceptual level: Provides both the mapping and the desired independence between the external and internal levels.
- (^) The objective of the three-level architecture is to separate each user’s
view of the database from the way the database is physically
represented.
Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models (^4)
External Level
- (^) Describes that part of the database that is relevant to each user.
- (^) Users’ view of the database.
- (^) Describes that part of database that is relevant to a particular user.
- (^) A user may require few attributes and may not need rest of the attributes. Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models 5
Internal Level
- (^) Physical representation of the database on the computer
- (^) Describes how the data is stored in the database.
- (^) It covers following things:
- (^) Storage space allocation for data and indexes
- (^) Record descriptions for storage (size)
- (^) Record placement
- (^) Data compression and encryption techniques Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models 7
Physical Data Organization
- (^) Below the internal level is the Physical Level.
- (^) This level is maintained by the Operating System under the direction of the DBMS.
- (^) Examples :
- (^) Fields are stored contiguously on disk or not. Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models 8
Objectives of Three-Level Architecture
- (^) Same data accessible to all users.
- (^) A user’s view is immune to changes made in other views.
- (^) Hide physical database storage details from users.
- (^) 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.
- (^) DBA should be able to change conceptual structure of database without affecting all users. Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models 10
Database Schema
- (^) The description of overall database is called database schema. - (^) External Schema - (^) Corresponds to different views of data - (^) Conceptual Schema - (^) Describes entities, attributes, relationships and constraints. - (^) Internal Schema - (^) It is a complete description of the internal model, including definitions of records, indexes and hashing functions. Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models 11
Data Independence Lecture 3 - DBMS Architecture, ANSI-SPARC architecture, Objectives, Database Schema, Languages and Data Models 13
Database Languages
- (^) Consists of two parts a Data Definition Language (DDL) and Data
Manipulation Language (DML).
- (^) Do not include constructs for all computing needs such as
conditional or iterative statements
Lecture 4 - Database Schema, Data Independence, Database Languages, Dataa Models, Conceptual Modeling 14
Data Manipulation Language (DML)
- (^) A language that provides a set of operations to support the basic data
manipulation operations on the data held in the database.
- (^) Data manipulation operations include:
- Retrieval/Selection
- (^) SELECT * FROM Employee
- (^) Insertion
- (^) Modification
- Deletion
- (^) Procedural DML
- Allows user to tell system what data is needed and exactly how to retrieve data.
- (^) Retrieves a record, processes it and, based on the results, retrieves another record that would be processed similarly, and so on.
- (^) Non-Procedural DML
- (^) Allows user to state what data is needed rather than how it is to be retrieved.
- (^) Single retrieval or update statement. Lecture 4 - Database Schema, Data Independence, Database Languages, Dataa Models, Conceptual Modeling 16
Data Models
- (^) A model is a representation of ‘real world’ objects and events, and their associations.
- (^) Data Model
- (^) Integrated collection of concepts for describing data, relationships between data, and constraints on the data in an organization. OR
- (^) Graphical systems used to capture the nature and relationships among data
- (^) The purpose of a data model is to represent data and to make the data understandable. If it does this, then it can be easily used to design a database.
- (^) Categories of data models include:
- (^) Object-based
- (^) Record-based
- (^) Physical.
- (^) Describe Data at internal level
- (^) Both object and record based describe Data at Conceptual and External Levels Lecture 4 - Database Schema, Data Independence, Database Languages, Dataa Models, Conceptual Modeling 17
Record-based Data Models
- (^) In this model, database consists of a number of fixed format
records and each record has a fixed number of fields.
- (^) There are three principal types of record-based logical data model
- (^) Relational model
- (^) Network model
- (^) Hierarchical model.
- (^) The hierarchical and network data models were developed almost
a decade before the relational data model, so their links to
traditional file processing concepts are more evident.
Lecture 4 - Database Schema, Data Independence, Database Languages, Dataa Models, Conceptual Modeling 19
Record-based Data Models
Relational Data Model
- This model is based on mathematical relations.
- Data and Relationships are represented by tables
- Each table has a number of columns with unique names. Lecture 4 - Database Schema, Data Independence, Database Languages, Dataa Models, Conceptual Modeling 20
