Chapter Eight
Business rules
Specifications that preserve the integrity of the logical data model.
Overlap rule
Specifies that an entity instance can simultaneously be a member of two (or more) subtypes.
Partial specialization rule
Specifies that an entity instance of the supertype does not have to belong to any subtype.
Disjoint rule
Specifies that if an entity instance of the supertype is a member of one subtype, it cannot simultaneously be a member of any other subtype.
Maximum cardinality
The maximum number of instances of one entity that may be associated with each instance of another entity.
Minimum cardinality
The minimum number of instances of one entity that may be associated with each instance of another entity.
Degree
The number of entity types that participate in a relationship.
Cardinality
The number of instances of entity B that can (or must) be associated with each instance of entity A.
Triggering operation
an assertion or rule that governs the validity of data manipulation operations such as insert, update and delete
Relationship
an association between the instances of one or more entity types that is of interest to the organization
What is the purpose of a conceptual data model?
to show as many rules about the meaning and inter-relationships among data as are possible
What is the secondary deliverable from the conceptual data modeling step within the Analysis phase?
a full set of entries about data objects that will be stored within the project dictionary, repository, or data modeling software
conceptual data model
a representation of organizational data
What are the four basic types of business rules?
1. Entity integrity - Each instance of an entity type must have a unique value that is not null 2. Referential integrity - rules about the relationships between entity types 3. Domains - constraints on valid values for attributes 4. Triggering operations - other rules that protect the validity of attribute values
What are the types of triggering operation?
1. Use rule - a concise statement of the business rules to be enforced by the triggering operation 2. Event - The data manipulation operation (insert, update, delete) that initiates the operation 3. Entity name - the name of the entity being accessed or modified 4. Condition - the condition that causes the operation to be triggered 5. Action - the action taken when the operation is triggered
Identifier
A candidate key that has been selected as the unique, identifying characteristic for an entity type.
Entity type
A collection of entities that share common properties or characteristics
Entity-relationship data model
A detailed, logical representation of the entities, associations, and data elements for an organization or business area.
Supertype
A generic entity type that has a relationship with one or more subtypes
Attribute
A named property or characteristic of an entity that is of interest to the organization.
Binary relationship
A relationship between the instances of two entity types. This is the most common form of relationship
Total Specialization rule
A rule that specifies that each entity instance of a supertype must be a member of some subtype in the relationship.
Repeating group
A set of two or more multivalued attributes that are logically related. Ex: information about employee dependents
Tertiary relationship
A simultaneous relationship among instances of three entity types
Entity instance
A single occurrence of an entity type
Subtype
A subgrouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroupings.
Composite attribute
An attribute that has meaningful component parts (attributes).
Optional attribute
An attribute that may not have a value for every entity (or relationship) instance with which it is associated.
Multivalued attribute
An attribute that may take on more than one value for a given entity (or relationship) instance. Ex: Employee skills
Required attribute
An attribute that must have a value for every entity (or relationship) instance with which it is associated.
Derived attribute
An attribute whose values can be calculated from related attribute values.
Candidate key
An attribute, or combination of attributes, that uniquely identifies a row in a relation.
Associative entity
An entity type that associates the instances of one or more entity types and contains attributes that are peculiar to the relationship between those entity instances; also called a gerund
Unary relationship
Association is maintained within a single entity
What is the primary deliverable from the conceptual data modeling step within the Analysis phase?
E-R diagram
What are the components that define a domain?
Name: Meaning: Data Type: Format: Range: Uniqueness: Null Support
Top-down approach
The process of deriving business rules for a data model from an intimate understanding of the business
Bottom-up approach
The process of deriving business rules for a data model from display screens, reports, and business focus handled within an existing system
Domain
The set of all data types and values that an attribute can assume
