Ch4 Entity Relationship Modeling
Order by
38 terms
Terms | Definitions |
|---|---|
 ER model | forms the basis of an ER diagram |
| ERD | represents conceptual database as viewed by end user |
| ERDs depict database's main components | - Entities - Attributes - Relationship |
| Entities | - Refers to entity set and not to single entity occurrence - Corresponds to table and not to row in relational environment |
| Chen and Crow's Foot mode | entity represented by rectangle with entity's name |
| Attributes | Characteristics of entities |
| Chen notation | attributes represented by ovals connected to entity rectangle with a line |
| Crow's Foot notation | attributes written in attribute box below entity rectangle |
| Required attribute | must have a value |
| Optional attribute | may be left empty |
| Domain | set of possible values for an attribute |
| Identifiers | one or more attributes that uniquely identify each entity instance |
| Composite identifier | primary key composed of more than one attribute |
| Composite attribute | can be subdivided |
| Simple attribute | cannot be subdivided |
| Single-value attribute | can have only a single value |
| Multivalued attributes | can have many values |
| Derived attribute | value may be calculated from other attributes |
| Relationships | -association between entities -between entities always operate in both directions -can be classified as 1:M -classification is difficult to establish if only one side of the relationship is known |
| Participants | are entities that participate in a relationship |
| Connectivity | Describes the relationship classification |
| Cardinality | Expresses minimum and maximum number of entity occurrences associated with one occurrence of related entity |
| Connectivity and Cardinality | Established by very concise statements known as business rules |
| Existence dependence | Entity exists in database only when it is associated with another related entity occurrence |
| Existence independence | Entity can exist apart from one or more related entities |
| Relationship Strength | -Weak (non-identifying) relationships -Strong (identifying) relationships |
| Weak (non-identifying) relationships | Exists if PK of related entity does not contain PK component of parent entity |
| Strong (identifying) relationships | Exists when PK of related entity contains PK component of parent entity |
| Weak Entities | -Existence-dependent -Primary key partially or totally derived from parent entity in relationship |
| Relationship Participation | -Optional participation -Mandatory participation |
| Optional participation | One entity occurrence does not require corresponding entity occurrence in particular relationship |
| Mandatory participation | One entity occurrence requires corresponding entity occurrence in particular relationship |
| Relationship Degree | Indicates number of entities or participants associated with a relationship -Unary relationship -Binary relationship -Ternary relationship |
| Recursive Relationships | Relationship can exist between occurrences of the same entity set,naturally found within unary relationship |
| Associative (Composite) Entities | -Also known as bridge entities -Used to implement M:N relationships -Composed of primary keys of each of the entities to be connected -May also contain additional attributes that play no role in connective process |
| Developing an ER Diagram | -Create detailed narrative of organization's description of operations -Identify business rules based on description of operations -Identify main entities and relationships from business rules -Develop initial ERD -Identify attributes and primary keys that adequately describe entities -Revise and review ERD (6) |
| Database Design Challenges | -Database designers must make design compromises -Important to meet logical requirements and design conventions -Design of little value unless it delivers all specified query and reporting requirements -Some design and implementation problems do not yield "clean" solutions (4) |
| Conflicting goals | design standards, processing speed, information requirements |
First Time Here?
Welcome to Quizlet, a fun, free place to study. Try these flashcards, find others to study, or make your own.