Midterm 2 Flashcards
Define:
conceptual database design
Conceptual database design involves modelling the collected information at a high-level of abstraction without using a particular data model of DBMS.
Define:
entity-relationship modelling
Entity-relationship modelling (ER modelling) is a top-down approach t o database design that models the data as entities, attributes, and relationships.
What is the relationship between conceptual database design and ER modelling?
The ER model is a type of conceptual database design.
What are the three stages of database design?
Conceptual
Logical
Physical
What happens at the conceptual level of database design?
Conceptual database design involves modelling the collected information at a high-level of abstraction without using a particular data model of DBMS.
e.g. UML or ER-modelling
What happens at the physical level of database design?
Physical database design is the process of selecting a DBMS.
What are some factors to consider when selecting a DBMS?
Features
Compatibility
Performance
Price
What are some factors to consider when selecting a DBMS?
Features
Compatibility
Performance
Price
What is the degree of a relationship type?
The number of entity types participating in the relationship.
Define:
entity type
An entity type is a group of objects with the same properties which are identified as having an independent existence.
Define:
relationship type
A relationship type is a set of associations among entity types. Each relationship type has a name that describes its function.
Entity names are usually ______ and relationship names are usually ______.
Entity names are usually nouns and relationship names are usually verbs.
Define:
recursive relationship
A recursive relationship is a relationship type where the same entity type participates more than once in different roles.
True or False:
It is not possible to have a relationship of degree one.
True. The minimum number is two.
Define:
attribute
An attribute is a property of an entity or a relationship type.
Define:
simple attribute
An attribute is simple if it contains a single component with an independent existence.
e.g. Social Insurance Number
Define:
composite attribute
An attribute is called composite if it consists of multiple components, each with an independent existence.
e.g. address can be broken into street, city, etc.
Define:
single-valued attribute
An attribute is a single-valued attribute if it consists of a single value for each entity instance.
e.g. salary
Define:
multi-valued attribute
An attribute is multi-valued if it may have multiple values for a single entity instance
e.g. people may have many different phone numbers
Define:
derived attributes
A derived attribute is one whose value is calculated from other attributes but is not physically stored.
Define:
candidate key
A candidate key is a minimal set of attributes that can uniquely identify each instance of an entity type.
Define:
primary key
A primary key is a candidate key that has been selected to identify each instance of an entity type.
Define:
composite key
A composite key is a key that consists of two or more attributes.
What is multiplicity?
The multiplicity is the number of possible occurrences of an entity type that may relate to a single occurrence of an associated entity type through a particular relationship.
For binary relationships, what are the three common types of multiplicities?
one-to-one (1:1)
one-to-many (1:* or 1:N)
many-to-many (: or N:M)
For relationships, what are the two participation constraints?
Cardinality, which is the maximum number of relationship instances for an entity participating in a relationship type.
Participation, which is the minimum number of relationship instances for an entity participating in a relationship type.
What is the difference between strong and weak entity types?
A strong entity type is an entity type whose existence is not dependent on another entity type, whereas a weak entity type is dependent upon another entity type.
What are the two possible choices for constraints on superclasses and subclasses?
Participation constraint
Disjoint constraint
What are the two possible choices for the participation constraints, and what do they mean?
Mandatory: a superclass member must be a member of one of its subclasses
Optional: a superclass member need not be a member of one of its subclasse.
What are the two possible choices for the disjoint constraints, and what do they mean?
And: a superclass member may be in more than one of its subclasse
Or: a superclass member may be in only one of its subclasses
What are the 8 steps when converting from ER to relational mapping?
- Strong entities
- Weak entities
- Relationships - 1:1
- Relationships - 1:*
- Relationships - :
- Multi-valued attributes
- N-ary relationship
- Subclasses
The ER model was proposed by ______ in ______
The ER model was proposed by Peter Chen in 1976
What happens at the logical level of database design?
Logical database design is the process of constructing a model of the information using a particular data model.
