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37 Cards in this Set
- Front
- Back
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What are the three stages of database development? |
- Requirements Analysis Stage - Component Design Stage - Implementation Stage |
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What are the 6 sources of requirements during the requirements analysis stage? |
- User Interviews - Forms - Reports - Queries - Use Cases - Business Rules |
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What are the most important elements of E-R Model? |
-Entities -Attributes -Identifiers -Relationships |
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What is an entity class? |
A description of the structure and format of the occurrences of the entity
- a collection of entites and is described by the structure of the entites in that class |
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What is an entity instance? |
A specific occurrence of an entity within an entity class. |
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What is an attribute to an entity? |
Describes the entity's characteristics and has a data type and properties. |
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What is an identifier to a entity? |
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Can identifiers be unique and nonunique? |
Yes |
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If an identifier is unique what MUST happen? |
The data value for the identifier must be unique for all instances. |
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What is a composite identifier? |
An identifier that consists of two or more atrributes |
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What are the levels of an entity attribute display? |
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How can entities be associated with one another? |
Through relationships |
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What is relationship degree? |
Defined as the number of entity classes participating in the relationship:
- Degree 2 is a binary relationship - Degree 3 is a ternary relationship |
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Define cardinality |
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Define Maximum cardinality |
The maximum number of entity instances that may participate in a relationship instance-one, many, or some other fixed number. |
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Define minimum cardinality |
The minimum number of entity instances that MUST participate in a relationship instance. |
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Define UML |
A set of structures and techinques for modeling and designing object oriented programs and applications |
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What are all the crow's foot symbols? |
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Define a weak entity |
An entity that cannot exist in the database without the existence of another entity |
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Define a strong entity |
any entity that is not a weak entity |
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Define a ID-Dependent weak entity |
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What is the relationship between a strong and weak entity called if the weak entity is ID dependent? |
An identifying relationship
Represented by a solid line. |
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The relationship between a strong entity is termed what if the weak entity is non-ID dependent? How is it represented? |
termed a nonidentifying relationship
Represented by a dashed line. |
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All ID dependent entites are weak entites, but are there other entities that are no ID dependent? |
Yes there are |
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A non ID dependent weak entity may have a single or composite identifier but the identifier of the parent entity will be a ______ ______ |
Foreign key |
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Define subtype |
A subtype entity is a special case of another entity called a super type |
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Define discriminator |
Decides which subtype is appropritae for a given instance |
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Are subtypes exclusive or inclusive? |
Both |
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If exclusive, a supertype relates to what? |
At most one subtype |
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If inclusive, a supertype relates to what? |
Can relate to one or more subtypes |
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The relationship that connect sueprtypes and subtypes are called what? |
IS-A relationships because a subtype is the same entity as the supertype. The identifier of a supertype and all of its subtypes is the same atrribute |
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Define recursive relationship |
A entity that has a relationship to itself |
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Define Use case |
Descriptions of the way users will employ the features and functions of the new information system. |
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Define relationship classes |
Associations among entity classes |
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Define relationship instances |
Associations among entity instances |
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What is the relationship that connects supertypes and subtypes called? |
IS-A, because a subtype is the same entity as the supertype. |
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Define HAS-A relationships |
Used because each entity has a relationship to a second entity instance. |
