Session Two
Attributes and Relationships

Topics

Relationships

Power Point: Relationships

When defining relationships:

Useful Relationship Name Pairs
  based on    the basis for
  brought from   the supplier of
  description of   for
  operated by   the operator for
  represented by   the representation of
  responsible for   the responsibility of
Do NOT use related or associated with as relationship names.
Why should you try to position a crowsfoot on the left end or the top end of the relationships line?

Layout Rules

  • Position higher volume, more volatile entities toward the top and left of the diagram.
  • Position lower volume, less volatile entities toward the bottom and right of the diagram.

    • Attributes

    Power Point: Attributes

    All entities are nouns, but not all nouns are entities.

    Entity Attribute

  • Anything about which information must be held
  • Possesses one or more attributes
  • If an entity has no attributes, it may be only an attribute
  • May have multiple occurrences associated with another entity via a relationship
    • Characteristics Characteristics
  • Qualifies an entity
  • Does not possess attribute(s) of its own
  • If an attribute has an attribute, then it is an entity or have no significance
  • Has a single value for each entity occurrence (no repeating groups)
    • Mandatory Attributes
  • A value must be known for each entity occurrence.
  • Tagged with *.
    • Optional Attributes
  • A value may be known for each entity occurrence.
  • Tagged with o.
    • Entity Instance Chart for the GARDEN CLUB MEMBER entity.

    Fill in the Attribute tags based upon the sample data.

    Attribute Name              
    Description of information Club ID
    number    		 Member's 
    last name    		 Position 
    or title    		 Sex Interest or 
    favorite area    		 Presentation
    Topic    		 City
    Tags               
    Sample 
    Data    		 110 Jones President F --- Trimming tulips Glendale
    301 Smith Treasurer M Roses --- Phoenix
    134 Gonzales --- F Desert plants Fertilizing Peoria
    340 Johnson Secretary M --- --- Phoenix
    589 Brown --- M Roses Transplanting Glendale
    Identify attributes by examining interview notes and by asking the user questions.

    Attributes may appear in interview notes as:

  • descriptive words and phrases.
  • nouns.
  • prepositional phrases (e.g. Salary amount for each employee).
  • possessive nouns and pronouns (e.g. Employee's name).
    • Questions to ask the user:
  • What information do you need to know or hold about entity x?
  • What information would you like displayed or printed about entity x?
  • Is this attribute really needed?
    • Examine documentation on existing manual procedures or automated systems to discover additional attributes and omissions.

    Paper Forms

  • Headings
  • Prompts
    • Computer Reports
  • Fields
  • Headings
  • Sort Orders
    • Computer Files Do NOT use attributes that are derived attributes or have attribute names that are plural.

    UID - Unique Identifier Definition

    Power Point: UIDs

    The combination of attributes and/or relationships that serve to uniquely identify an occurrence of an entity.

    An entity MUST have a UID or it is NOT an entity.

    An Entity can be uniquely identified through a relationship.

  • Single attribute
  • Use the # to indicate the attribute is part of the entity's UID - Octothorp
  • Sometimes you will need to create an artificial attribute like employee ID.
  • Compound attribute
  • More than one attribute.
  • Composite
  • Combination of attributes and relationships
  • Use the | to indicate that a relationship is part of the entities UID.
  • A relationship included in a UID must be mandatory and one and only one in the direction that participates in the UID.
    • All components of a UID must be mandatory *
    Therefore, tag each UID attribute with #*

    An entity may have more than one UID.  If that is the case one is the primary UID and the other(s) is the secondary and is indicated with #(2)  or (#)

    Go back to the GARDEN CLUB MEMBERS above and select a UID.

    Additional Practice

    Summary

    1.  Identify each entity.

    2.  Consider the Relationships

  • Which of the relationships help identify the entity?
  • Are there missing relationships that help identify the entity?
  • Does the relationship help uniquely identify the entity?

    • Is the relationship mandatory and one and only one in the direction from the entity?
    3.  Evaluate the Attributes
  • What mandatory attributes identify the entity? Seek out additional at-tributes that help identify the entity. Consider creating artificial attributes for identification.
  • Does an attribute uniquely identify the entity?
  • What combination of attributes uniquely identify the entity?
    • 4.  Validate the UID
  • Examine sample data. Does the selected combination of attributes and relationships uniquely identify each instance of an entity?
  • Are all the attributes and relationships that are included in the UID mandatory?