Unit 11 : Extended Entity Relationship Model Flashcards
What is the common characteristics for data model?
- Conceptual simplicity without compromising the semantic completeness of the database
- Represent the real world as closely as possible
- Representation of real-world transformations must comply with consistency and integrity characteristics of any data model
What is data abstraction?
- Ways of classifying data models
What are the process of data abstraction?
- Many processes begin at high level of abstraction and proceed to an ever increasing level of detail
Who defined a framework for data modeling based on the degrees of data abstraction?
- American National Standards Institute ( ANSI )
- Standards Planning and Requirements Committe ( SPARC )
List out the framework for data modeling based on degrees of data abstraction ( 3 )
- External
- Conceptual
- Internal
Who view the external model of the data environment?
- End Users
What does the external model requires?
- The modeler subdivide set of requirements and constraints who functional modules that can be examined within the framework of their external models
What is the advantages of the external model? ( 4 )
- Easy to identify specific data required to support each business unit’s operations
- Facilitates designer’s job by providing feedback about the model’s adequacy
- Creation of external models helps to ensure security constraints in the database design
- Simplifies application program development
What does the conceptual model represent?
- The global view of the entire database
What is the representation of data in the conceptual model?
- Representation of data as viewed by the entire organization
What is the conceptual model mainly focued on?
- The basis for indentification and high-level description for main data objects, avoiding details
What is the most widely used conceptual model?
- Entity Relationship Model
What does the conceptual model provides?
- A relatively easily understood macro level view of data environment
How does the conceptual model is independent of both software and hardware? ( 3 )
- Does not depend on the DBMS software used to implement the model
- Does not depend on the hardware used in the implementation of the model
- Changes in either hardware or DBMS software have no effect on the database design at the conceptual level
What models is more technical than the conceptual model?
- The internal model
How does the Internal Model represents the diagram?
- Representation of the database as “seen” by DBMS
- Represents the database from the perspective of DBMS
- Maps the conceptual model to the DBMS
What depicts a specific representation of an internal model?
- Internal Schema
What model operates at lowest level of abstration? ( Mention the name and what it describe )
- The Physical Model
- Describing the way data are saved on storage media such as disks or tapes
Is the physical model dependent on both software and hardware?
- Yes
- It takes into account the particular requirements and limitations of the devices, such as storage capacities, access speeds, and memory.
What is the requirement for database designers to implement database design at the physical model?
- Requires that database designers have a detailed knowledge of the hardware and software used to implement database design
What is Extended Entity Relationship model?
- The result of adding more semantic constructs to original entity relationship model
- It is called EERD
List out the key concepts in EER (
- Supertypes and Subtype Relationship
- Specialization and Generalization
- Inheritance
What type ( super / sub ) contains common characteristics?
- Supertype
What type ( super / sub ) contains unique characteristics of each entity subtype?
- Subtypes
What type ( super / sub ) is a generic entity type that is related to one or more entity subtypes?
- Supertype
What does specialization hierarchy depicts?
- Arrangement of higher-level entity supertypes ( parent entities ) and lower-level entity subtypes ( child entities )
How are relationships sometimes described in a specialization hierarchy?
- “IS-A” relationship
Can a subtype exist independently of its supertype?
- No, a subtype can exist only within context of supertype and every subtype can have only one supertype to which it is directly related
Can specialization hierarchies have multiple levels?
- Yes, they can have many levels of supertype/subtype relationships.
What is attribute inheritance in specialization hierarchies?
- Attribute inheritance means that subtypes automatically inherit attributes from their supertype
What is a subtype discriminator?
- The attribute in supertype entity that determines to which entity subtype each supertype occurrence is related
What is the default comparison condition for subtype discriminator ?
- Equality Comparison
What subtypes ( disjoint , overlapping ) is also known as non-overlapping subtypes?
- Disjoint Subtypes
What is a disjoint subtypes?
- Subtypes that contain unique subset of supertype entity set
What is a overlapping subtypes?
- Subtypes that contain nonunique subsets of supertype entity set
What does completeness contratint specifies?
- Specifies whether each entity supertype occurrence must also be member of at least one subtype
- Which can be partial or total
What does specialization do?
- It provides the top down process of identifying lower-level, more specific entity subtypes from higher-level entity supertype
- It is based on grouping unique characteristics and relationships of the subtypes
What does generalization do?
- Provides botton-up process of identifying higher-level, more generic entity supertype from lower-level entity subtypes
- It is based on grouping common characteristics and relationships of the subtypes
What does inheritance enables?
- Enables entity subtype to inherit attributes and relationships of supertype
Do all entity subtypes inherit their primary key attribute from their supertype?
- Yes, all entity subtypes inherit their primary key attribute from their supertype, ensuring uniqueness across the hierarchy.
How is the relationship between a supertype and its subtype(s) depicted at the implementation level?
- At the implementation level, the supertype and its subtype(s) maintain a 1:1 relationship in the specialization hierarchy.
