DBTG and Database Standards

Network Model

• Developed as an alternative to the hierarchical model
• Handles more relationship types than the hierarchical model
• Provides data access flexibility and promotes database integrity
• Conforms to standards
• Uses navigational language with constructs like FIND, FIND member, FIND owner, FIND NEXT within set, GET, etc.
• Allows programmers to navigate optimally through the database

Disadvantages of Network Model

• Navigational and procedural nature of processing
• System complexity
• Lack of structural independence
• Database contains a complex array of pointers that thread through a set of records
• Little scope for automated "query optimization"

Relational Model

• Developed by E.F. Codd (IBM) in 1970
• First commercial system in 1981-82
• Created to represent complex data relationships more effectively than the hierarchical model
• Improves database performance
• Imposes a database standard

Crucial Database Components (DBTG report)

• Schema: Conceptual organization of entire database as viewed by the database administrator
• Subschema: Defines database portion seen by application programs that produce desired information from data contained within the database
• Data Management Language (DML): Defines data characteristics and data structure in order to manipulate the data
• Schema Data Definition Language (DDL): Enables database administrator to define schema components
• Subschema DDL: Allows application programs to define database components that will be used
• DML: Manipulates database contents

Network Model Basic Structure

• Resembles hierarchical model
• Collection of records in 1:M relationships
• Relationship is called a Set: Set is composed of at least two record types
• Owner: Equivalent to the hierarchical model’s parent
• Member: Equivalent to the hierarchical model’s child

Network Model Advantages

• Ability to model complex relationships and represents semantics of add/delete on the relationships
• Crow’s foot and Chen Notations can be used for graphical representation
• Entity is mapped to a relational table
• Entity instance (occurrence) is a row in the table
• Entity set is a collection of entities at any time
• Connectivity labels types of relationships
• Diamond connected to related entities through a relationship line
• Relationships are expressed using Chen notation
• Relationship name is written inside the diamond

Entity Relationship Model

Advantages

• Exceptional conceptual simplicity
• Visual representation
• Effective communication tool
• Integrated with the relational data model

Disadvantages

• Limited constraint representation
• Limited relationship representation
• No data manipulation language
• Loss of information content

Object-Oriented Model

• Developed by Hammer and McLeod in 1981 as a semantic data model (SDM)
• Modeled both data and their relationships in a single structure known as an object
• Basis of object-oriented data model (OODM)
• OODM becomes the basis for the object-oriented database management system (OODBMS)
• Object is described by its factual content
• Includes information about relationships between facts within object and relationships with other objects
• Subsequent OODM development allowed an object to also contain operations
• Object becomes basic building block for autonomous structures

Object-Oriented Model Basic Structure

• Object: abstraction of a real-world entity, contains operations and is self-contained and forms a basic building-block for autonomous structures
• Attributes describe the properties of an object
• Objects that share similar characteristics are grouped in classes
• Classes are organized in a class hierarchy
• Inheritance is the ability of an object within the class hierarchy to inherit the attributes and methods of classes above it

Advantages of Object-Oriented Model

• Adds semantic content
• Visual presentation includes semantic content
• Database integrity
• Both structural and data independence
• Persistent programming languages based OODB target applications of that form that have high performance requirements