Flashcards
SCC 201 - The ER model
Cards in this deck (17)
- 1What does the entity relational model allow?Allows analysis, specification and design of database structure
– Independent of data model of underlying database system, for example, relational, object-oriented, etc - 2What is the entity relational model?An entity relationship model, also called an entity-relationship (ER) diagram, is a graphical representation of entities and their relationships to each other, typically used in computing in regard to the organization of data within databases or information systems.
- 3What are the three basic concepts of the entity relational model?– Entities
– Relationships
– Attributes - 4Who does the entity relational model aid?It's an aid for database designer
- 5Define entities in relation to the ER model?– Data about a specific object: real or abstract
- 6Define relationships in relation to the ER model?– Associations among entities
- 7Define the degree of a relationships in relation to the ER model and describe what two, three and n degree mean?– This is the number of participating entity types
A relationship of degree
• Two is called a binary relationship
• Three is called a ternary relationship
• n is in general referred to as an n-ary relationship - 8Define recursive relationships in relation to the ER model?a recursive relationship is one where participating entity types are the same
- 9What is cardinality ratio in relation to ER model?– Number of relationship instances an entity can participate in
- 10Define what this following cardinaility ratios represent? 1:1 1:N M:N– 1:1 represents a one-to-one binary relationship
– 1:N represents a one-to-many binary relationship
– M:N represents a many-to-many binary relationship - 11Define attributes in relation to the ER model?– Properties describing an entity
- 12Define key attributes in relation to the ER model?– Have unique values for each instance of an entity type
- 13What are atomic attributes in relation to the ER model and give an example?– Are indivisible
– In our example, Department Name and Course Name are two atomic attributes - 14What are composite attributes in relation to the ER model and give an example?– Can be divided into smaller subparts that represent more basic attributes with independent meaning
In our example, Student Name is a composite attribute as it can be subdivided into First Name and Last Name - 15What are singled valued attributes in relation to the ER model and give an example?Single-valued attributes
– Have single value for particular instance of entity type
– In our example,
NoOfEmps is single-valued attribute of Department - 16What are multi-valued attributes in relation to the ER model and give an example?– Can have set of values for particular instance of entity type
– In our example,
Location is multi-valued attribute of Department - 17—
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- Flashcards on SCC 201 - The ER model, created by Ayo Olutobi on 31/03/2017.
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- Ayo Olutobi
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