2. modelling Flashcards
What is a model in data modeling?
A model is an abstraction of reality, constructed based on a specific point of view and level of abstraction.
What are business rules?
Business rules are statements that define or constrain aspects of a business, establishing structure and guiding behavior using business language.
What characteristics define a good business rule?
They are declarative, precise, atomic, consistent, expressible, distinct, and business-oriented.
What constitutes a good data name?
A good data name is business-related, meaningful, unique, readable, based on approved vocabulary, and follows standard syntax.
What are data definitions?
They are concise explanations of terms or facts gathered with system requirements and refined iteratively, often with supporting diagrams.
What are the main constructs of an E-R model?
The main constructs are entities, relationships, and attributes.
What is an entity in data modeling?
An entity is an object with many instances and multiple attributes that represents something to be modeled, excluding system users or outputs.
What are the three levels of a database system implementation?
The conceptual model (an ER diagram), the logical model (a relational model), and the physical implementation (actual database objects).
How are attributes classified in data modeling?
Attributes are classified as required versus optional, simple versus composite, single-valued versus multivalued, stored versus derived, and as identifier attributes.
What is an identifier in data modeling?
An identifier, or key, is an attribute or set of attributes that uniquely identifies an entity instance and should be stable and non-null.
What is the difference between a relationship type and a relationship instance?
A relationship type is a general association between entity types, while a relationship instance is a specific occurrence of that association; relationships may also have their own attributes.
What are cardinalities and cardinality constraints in relationships?
Cardinalities specify whether relationships are one-to-one, one-to-many, or many-to-many, while cardinality constraints define the minimum and maximum associations between entities.
What is an associative entity?
An associative entity is used to model many-to-many relationships that include additional attributes, breaking them into two one-to-many relationships and ensuring data integrity.
What distinguishes strong and weak entities?
Strong entities exist independently with unique identifiers, whereas weak entities depend on strong entities and have partial identifiers linked via identifying relationships.
When should attributes be added to a relationship?
Attributes should be added when the relationship has descriptive details, requires a unique identifier, represents an event or transaction, includes temporal aspects, differentiates multiple relationship types, or enforces business rules.
When should you not add attributes to a relationship?
Do not add attributes if the relationship is simple, if the attributes logically belong to one of the related entities, or if adding them would create unnecessary complexity.
What is the purpose of an associative entity in relational modeling?
It converts a many-to-many relationship into two one-to-many relationships while capturing additional attributes and maintaining referential integrity.
