Week 1 Flashcards
What is a Database Management System (DBMS)?
Provides efficient, reliable, convenient, safe, multi-user friendly storage and access to massive amounts of persistent data.
What is an Entity Relationship Model
A graphical representation of the logical view of a Database
What is an Entity?
An object that has distinguishable properties,
An entity must have attributes
Entity use Rectangular shape
What is an entity set?
A conceptual representation of entities w.r.t the same set of attributes
What is an attribute?
Property that distinguishes an entity, is represented with an oval shape
What attribute distinguishes an entity (the whole row) within the entity set Car?
“Model” uniquely identifies an entity (the whole row) within this entity set.
The attribute that uniquely identifies an entity within this entity set is called a “key attribute” (represented with solid underlines)
What are Candidate keys? In the photo, which attributes that can be called Candidate keys?
Candidate keys are the set of all possible key attributes. In the photo above, (Model,Length)
What is a Derived attribute? What is a Multi-valued attribute?
A derived attribute is an attribute that is computed from another attribute. Represented with a dashed line.
A multi-valued attribute is an attribute that have multi-values, represented with double lines.
What is a Relation?
A logical model for associating two or more Entities.
What is a Relation set?
It covers all such relations between two or more Entity sets. It is represented with a diamond.
What is a Degree of a relationship set?
The number of entity sets that participate in a relationship
What is a Binary relationship?
A relationship that involves two entity sets.
What is a Ternary relationship sets?
A relationship that involve three entity sets
What is a Unary relationship set?
A relationship that involves an entity that have a relationship with its own entity
What are the 4 types of cardinalities in a relationship?
- 1:1 (one-to-one)
- 1:N (one-to-many)
- N:1 (many-to-one)
- N:N (many-to-many)
What is the cardinality of this relationship?
1:1
What is the cardinality of this relationship?
1:N, One car be repaired by many mechanics, A mechanic can repair one car.
What is the cardinality of this relationship?
N:1 One car be repaired by a mechanic, A mechanic can repair many cars.
What is the cardinality of this relationship?
N:N, One car can be repaired by many mechanics, A mechanic can repair many cars
What is a Total Participation?
Shows that it is mandatory for the entity who link with a total participation (Identified with a double line) to be in the relationship
What is a Partial Participation?
Shows that it is not compulsory for entity that linked with a partial participation (identified with a single line) to be in the relationship
What is a weak entity?
A weak entity is an entity that is dependent on a strong entity, meaning that a weak entity cannot be in the table without it strong entity. It is denoted with a double line square.
The weak entity does not have a primary key, instead, it uses a compound key which is a concatenation of its attribute with the primary key of its dependent entity. The weak entity key used in the compound key is denoted with a dashed underline.
What is an ISA?
An extended ER Hierarchies that is used for adding descriptive attributes specific to a subclass.
