IFB130 Lecture Notes - Lecture 2: Unified Modeling Language, Conceptual Schema, Modeling Language
19 Oct 2018
School
Department
Course
Professor
Lecture 2 - Entity Relationship Modelling
Wednesday, 1 August 2018
12:12 PM
ER - Motivations
• Conceptual Design is an important phase in designing a successful database application
• These are important to communicate database designs to non-technical users
o Lack of communication may result in user's data requirements being missed or incorrect
requirements being captured.
• ER model is one of the most widely used method for conceptual design
• Can be mapped to a Relational Schema.
Weeks 2-3: Build the Entity Relationship Model
Entity Relationship Diagram (ERD)
• Conceptual data model
• Used to model and design relational databases, in terms of logic and business rules
• Visual translation of use case into entities, their relationships and attributes
Unified Modelling Language (UML)
• General purpose, developmental, modelling language used in software engineering
• This is the modelling 'language' we will be using in IFB130 to model ERDs.
Entities
• Entity type
o Group of objects with the same properties and independent existence
• Entity occurrence
o Uniquely identifiable object of an entity type
E.g. Entity type could be 'dog', entity occurrences of 'dog' could be 'Fido the Golden Retriever',
'Jerry the German Shephard', and so on.
Relationships
• Relationship type
o Set of meaningful associations among entity types
• Relationship occurrence
o Uniquely identifiable association, which includes on occurrence from each participating
entity type
Relationship type: E.g. A 'customer' <watches> 'movie'
Relationship occurrence: E.g. A customer 'Sam' <watches> movie 'Batman'.
Relationship Degrees
• Degree
o Describes the number of participating entities in a relationship.
• 2 degree relationship I called a binary relationship
• 3 degree relationship is called a ternary relationship
• 4 degree relationship is called a quaternary relationship
• Recursive relationship
o A relationship type where the same entity type participates more than one and in
different roles
Document Summary
Entity relationship diagram (erd: conceptual data model, used to model and design relational databases, in terms of logic and business rules, visual translation of use case into entities, their relationships and attributes. Unified modelling language (uml: general purpose, developmental, modelling language used in software engineering, this is the modelling "language" we will be using in ifb130 to model erds. Entities: entity type, group of objects with the same properties and independent existence, entity occurrence, uniquely identifiable object of an entity type. Entity type could be "dog", entity occurrences of "dog" could be "fido the golden retriever", Relationships: relationship type, set of meaningful associations among entity types, relationship occurrence, uniquely identifiable association, which includes on occurrence from each participating entity type. Staff member supervises staff member, staff member is the supervisee of staff member. "cat", d. o. b would be a single valued attribute: multi-valued attribute, an attribute that holds multiple values for each occurrence of an entity type.
