IM - Unit 3

• Conceptual Data Model


  represents data from the viewpoint of the organization, independent of any technology that will be used to implement the model.
• ER Model


  is a detailed, logical representation of the data for an organization or for a business area
• entities in the business environment, the relationships (or associations) among those entities, and the attributes (or properties) of both the entities and their relationships


  The E-R model is expressed in terms of
• ER Model


  is normally expressed as an entity-relationship diagram (E-R diagram, or ERD), which is a graphical representation of an E-R model.
• entity type


  basic concept of the ER model is the
• entity type


  represents a group of "objects" in the "real world" with the same properties.
• entity occurrence


  Each uniquely identifiable object of an entity type is referred to simply as an
• a rectangle, labeled with the name of the entity, which is normally a singular noun


  Each entity type is shown as a
• Strong Entity Type


  An entity type that is not existence-dependent on some other entity type.
• Weak Entity Type


  An entity type that is existence-dependent on some other entity type
• relationship type


  is a set of associations between one or more participating entity types; is given a name that describes its function.
• relationship occurrence


  indicates the particular entity occurrences that are related.
• participants


  The entities involved in a particular relationship type are referred to as
• degree of a relationship


  The number of participants in a relationship type is called the; indicates the number of entity types involved in a relationship.
• complex relationship


  is used to describe relationships with degrees higher than binary
• Binary


  relationship degree of two
• Ternary


  relationship degree of three
• Quaternary


  relationship degree of four
• Recursive Relationship


  A relationship type in which the same entity type participates more than once in different roles
• unary relationships


  Recursive relationships are sometimes called
• role names


  to indicate the purpose that each participating entity type plays in a relationship; can be important for recursive relationships to determine the function of each participant; used when two entities are associated through more than one relationship
• attributes


  The particular properties of entity types are called
• domain


  Each attribute is associated with a set of values called a; defines the potential values that an attribute may hold and is similar to the domain concept in the relational model
• Simple Attributes

  Composite Attributes

  Single-valued Attribute

  Multi-valued Attribute

  Derived Attribute


  Types of Attributes
• Simple Attributes


  An attribute composed of a single component with an independent existence
• Composite Attribute


  An attribute composed of multiple components, each with an independent existence
• Single-valued Attribute


  An attribute that holds a single value for each occurrence of an entity type
• Multi-valued Attribute

  An attribute that holds multiple values for each occurrence of an entity type
• Derived Attributes


  An attribute that represents a value that is derivable from the value of a related attribute or set of attributes, not necessarily in the same entity type
• - Candidate Key

  - Primary Key

  - Composite Key


  Types of Key Attributes
• Candidate Key


  The minimal set of attributes that uniquely identifies each occurrence of an entity type
• Primary Key


  The candidate key that is selected to uniquely identify each occurrence of an entity type
• Composite Key


  A candidate key that consists of two or more attributes
• Multiplicity


  The main type of constraint on relationships is called
• Multiplicity


  the number (or range) of possible occurrences of an entity type that may relate to a single occurrence of an associated entity type through a particular relationship
• Multiplicity


  constrains the way that entities are related. It is a representation of the policies (or business rules) established by the user or enterprise. Ensuring that all appropriate constraints are identified and represented is an important part of modeling an enterprise
• - Cardinality

  - Participation


  2 constraints of multiplicity
• Cardinality


  describes the maximum number of possible relationship occurrences for an entity participating in a given relationship type
• 1:1

  1:N

  N:1

  N:N

  Types of Cardinality
• Participation


  determines whether all or only some entity occurrences participate in a relationship.