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Semantic Object Model
Define semantic objectsUse semantic object diagrams to build
data modelsDefine and illustrate the 7 basic types
of semantic objectsCompare semantic object and entity-
relationship models
Data models as lenses
Defining Semantic Objects
SOM <> OO DB processing!Objects: things to be representedSemantic: carry some meaningAttributesIdentifiers
Semantic Object
“A named collection of attributes that sufficiently describes a distinct identity” sufficient description means that the attributes
represent all of the characteristics that users need
distinct identity is something that users recognize as independent and separate
Need not be physical
SO class vs. instance
Distinct?Distinct?Physical?Physical?
Attributes
Types Simple Group Object
CardinalityDomains
Physical Semantic
Attribute Domains
Description of an attribute’s possible values Physical Description
type and length of data, constraints can be enumerated list example: RoomNumber in dept. catalog? (How
about the campus catalog?)
Semantic Description (logical) function or purpose of the attribute example: RoomNumber?
Let’s build an object
E.g., SOCCER-PLAYER?Properties?Instance?Name of semantic object?Name of semantic object instance?Some property domains...
Physical? Semantic?
Semantic Object Diagram
Object Name
Group Attribute
Simple Attribute
Cardinality(min.max)
UniqueIdentifier
STUDENT
StudentIDStudentName
FirstNameInitialLastName
PhoneNumber
DEPARTMENT
0.1
1.1
1.N
1.1
1.1
ID
ID
Object Attribute(or Object Link)
Non-uniqueGroup Identifier
1.1
1.1
What is the cardinality of an identifier?What is the cardinality of an identifier?
Domain specifications
Object specifications
Domain specifications
(a)
Paired attributes
Object links are always pairedNo 1-way object relationships
Semantic Object Views
Roundtable Exercise
Form groups of 3 or 4; introduce yourselfLabel yourselves: 1,2,3...One sheet of paper and pencil per groupIn turn:
one person describes an object from the following report
another person draws its diagram on the sheet (1 or 2 attributes)
rotate!
Invoice Date: 08/15/98 FILIPPO MENCZER MCI Dumb Foreigner plan______________________________________________________________________________Fees $6.05Long Distance Calls $15.50International Long Distance Calls $105.45______________________________________________________________________________Total Current Charges $127.00
International Long Distance ______________________________________________________________________________MCI Calling Plan Calls from 319-555-PROF: DATE TIME RATE TO/FROM NUMBER MIN AMOUNT
______ ______ ______ ________________ ______________ ________ __________Jul 29 10:44A S TO SWTZRLAND 41274812900 7 9.73Aug 02 10:39A S TO ITALY 39336850757 4 6.08
03 12:52P S TO ITALY 39068073418 19 28.8808 01:07P X TO ITALY 39336850757 19 28.8814 12:48P S TO SWTZRLAND 41274812900 12 16.68
______________________________________________________________________________Total International Long Distance $105.45
Form reverse-engineering
Semantic Object Types
SimpleCompositeCompoundHybridAssociationParent/SubtypeArchetype/Version
Simple Objects
Only single-valued, non-object attributes
Composite Objects
One or more multi-valued, non-object (simple or group) attributes
Composite Objects
Multi-valued groups can be nested
Is this correct?
Compound Objects
Have at least one object attribute
Object attributes are always in pairs (here 1:1)
Compound Objects
Designer must find out about cardinalities of paired object properties
4 types of compound objects (max card.)
1 example of each?
Hybrid Objects
Combination of objects of two typesAt least one multi-valued group attribute
containing an object link
Hybrid vs. Compound Objects
What’s wrong with this?
Hybrid Object Max Cardinality
ITEM in one or more SALES-ORDERS?ITEM in one or more LineItems within one
SALES-ORDER?
Association Objects
Relates two or more objects and stores data that pertains to the relationship
Typical in resource assignments
May or may not have its own ID
Parent/Subtype Objects Generalized object that
logically contains one or more subcategories
Avoid duplication & NULLsSubtype object attribute =
IS-A attributeInheritance
Subtype object inherits parent attributes
Parent acquires all attributes of its subtypes
Multiple Subtypes
A parent may have more than one subtype
For exclusivity, place subtype object attributes into a subtype group
X.Y.Z X=min group cardinality Y=min attribute count Z=max attribute count
Nested Subtypes
Archetype/Version Objects
Archetype object produces other objects that represent versions, releases, or editions of the archetype
Version object ID contains archetype object link
E-R vs. SO Models
Objects show context (boundaries)Objects contain multi-varied attributesObjects contain other objectsEasier documentation (metadata)
E-R vs. SO Models
which makes better sense to you?
Invoice Date: 08/15/98 FILIPPO/COLLEEN MENCZER Service Summary ______________________________________________________________________________MCI One Advantage plan fee (07/25/98 to 08/14/98) $3.03Long Distance $15.50International Long Distance $105.45Other Fees $6.05______________________________________________________________________________Total Current Charges $130.03
International Long Distance ______________________________________________________________________________MCI Calling Plan Calls from 319-555-PROF: DATE TIME RATE TO/FROM NUMBER MIN AMOUNT
______ ______ ______ ________________ ______________ ________ __________Jul 29 10:44A S TO SWTZRLAND 41274812900 7 9.73Aug 02 10:39A S TO ITALY 39336850757 4 6.08
03 12:52P S TO ITALY 39068073418 19 28.8808 01:07P X TO ITALY 39336850757 19 28.8814 12:48P S TO SWTZRLAND 41274812900 12 16.68
______________________________________________________________________________Total International Long Distance $105.45
Form reverse-engineering
INTERNATIONAL Country
RateINVOICE P
CUSTOMERID NameID PhoneNumber
PlanINVOICE 1.N
A data model from this form
LONG-DISTANCE Rate
INVOICE P
0.N
1.1
1.1.1
INVOICEID InvoiceID
DateCUSTOMER
Fee 0.N
CallDateTimeNumberLONG-DISTANCE 0.ST
INTERNATIONAL 0.ST
MinutesAmount