Week 3 Flashcards
What are the two approaches to database design?
Normalisation (bottom-up) and Semantic Data Modelling (top-down)
What is normalisation (Bottom-Up) in database design?
this has one table describing all relevant data and serves as the starting point. Consists of multiple tables which are decomposed until 3NF.
What is Semantic Data Modelling (Top-down) in database design?
Knowledge about business processes and information needs is used to create a diagram (entity relationship diagram). This describes the data and its relationships that are to be recorded in a database.
What is Entity Relationship Modelling (ERM)
ERM is a modelling notation used to model the characteristics and relationships of data. Useful to formalize and visualize the structure of data for implementation of databases.
What does ERD consist of?
Entity, Attributes and Relationships
What are entities in ERD?
Real word things we want to record data about
What are attributes in ERD?
Characteristics of entities, all entities should have the same in common. Predefined value range.
What are relationships in ERD?
Associations between entities. Defines a set of relationships among entities from different entity types. A relationship type can also have an attribute.
What are cardinalities?
Expresses the number of entity occurrences associated with one occurrence of a related entity.
What is an entity type?
collection of entities with similar characteristics. The name should be a generic term describing all entities of the collection.
What is a key?
The identifying attribute - it is an attribute that unambiguously identifies an entity. A key can be a combination of multiple attributes.
What are the 4 meanings of carinalities?
1 = {1}
C = {0, 1}
N = {1, 2, …, n}
NC = {0, 1, 2, …, n}
What is an 1:1 relationship?
Everyone uses one
What is a C:C relationship?
Everyone can have 1 or 0
What is an example of 1:N relationship?
Mother & child