Chapter 2 DBMS
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The document describes a three-level database architecture consisting of an external, logical, and internal model. It also discusses logical data models including the semantic and record-based models. Key points covered include the relational, hierarchical, and network models as well as the importance of data independence.
Chapter 2 DBMS
- 1. The Three-level Architecture I. External model II. Logical or conceptual model III. Internal or physical model Logical Data Models I. Semantic data model II. Record based model DATABASE ARCHITECTURE
- 2. THE THREE-LEVEL ARCHITECTURE External model Logical Or Conceptual Model Internal Or Physical Model
- 4. EXTERNAL LEVEL • The external level interacts directly with the user (end users or application programs). It changes the data coming from the conceptual level to a format and view that is familiar to the users. • Consists of many user models or views • Has external records - records seen by users • May include calculated or virtual data • Devide in external schemas (sub-schemas) • Used to create user interface
- 5. LOGICAL OR CONCEPTUAL MODEL The conceptual level defines the logical view of the data. • All entities, attributes, relationships represented • Includes all record types, data item types, relationships, semantic information, security and integrity information • Described in logical schema
- 6. INTERNAL LEVEL • The internal level determines where data is actually stored on the storage devices. • The DBMS and Operating System View • Physical implementation level • Includes data structures, file organizations used by DBMS • Depends on what DBMS is used
- 7. WHAT IS DATA INDEPENDENCE •Techniques that allow data to be changed without affecting the applications that process it.
- 8. Slide 2- 8 TYPES OF DATA INDEPENDENCE • Logical Data Independence: • The capacity to change the conceptual schema without having to change the external schemas and their associated application programs. • Physical Data Independence: • The capacity to change the internal schema without having to change the conceptual schema. • For example, the internal schema may be changed when certain file structures are reorganized or new indexes are created to improve database performance
- 10. ¤ In this model database is structured in fixed-format records of several types. ¤ They allow the designer to develop and specify the logical structure and provide some options for implementation of the design ¤ It describes the data at the conceptual and view levels both. ¤ Specify overall logical structure of the database
- 11. I. Hierarchical Model II. Network Model III. Relational Model
- 13. ¤ Oldest ¤ Like a structure of a tree ¤ Branches represent fields ¤ Nodes represent record ¤ Structure contains levels, or segments. ¤ Higher layer is perceived as the parent of the segment directly beneath it, which is called the child
- 14. S1001 Ali Ahmad Computer Science 60 Csc01A Intro to Algo Talha TuF10 N45 S1002 Kamal Khan Computer Science 60 S1008 Noman Ch Computer Science 60
- 16. ¤ Like hierarchical model ¤ But may have many to many relation ¤ It allows a record to have more than one parent ¤ Replaces the hierarchical tree with a graph
- 17. S1001 Ali Ahmad Computer Science 60 Csc01A Intro to Algo Talha TuF10 N45 S1002 Kamal Khan Computer Science 60 S1008 Noman Ch Computer Science 60 Mth01A Calculus I Mutiullah MW9 R25
- 18. :- A student taking two classes :- A teacher teaches different classes :- An employee works for two departments
- 20. ¤ Proposed by E.F. Codd ¤ Uses relations ¤ Contains tables ¤ Tables represent relationships ¤ Columns represent attributes ¤ It’s better than others
- 21. STDID STDNAME MAJOR CREDITS S1001 Ali Ahmad Computer Science 60 S1002 Kamal Khan Math 40 S1003 Shoaib Mansoor Computer Science 60 C_ID CNAME PROF SCHED ROOM Mth01A Calculus I Mutiullah MW9 R25 Csc01A Intro to Algo Talha TuF10 N45 Csc01B Programming I Imran TuThF9 N40 Student - Table Enrollment - Table Class - Table C_ID STDID Grade Csc01A S1001 B+ Csc01B S1001 A Mth01A S1002 B Csc01A S1002 B