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MetaData“Data about Data”
College of Alameda
Copyright © 1999 Patrick McDermott
I never met a data
I didn’t like.—PMcD
“Data is, Data are.” In human language, “One word can mean more than one thing. This flexibility provides a deep well of nuance and beauty; it is a foundation of poetry. But it leads only to trouble when you are trying to build software.”—Scott Rosenberg, Dreaming in Code
One cannot givewhat one does not have
One cannot have
what one has no
place to keep
Nēmō dat qua nōn habet.
The Sour of Babel
Illustrates the Metadata obstacleto the Semantic Web:
We need to call the Same thingby the Same name,
Different thingsby Different names
Pietr Brueg(h)el (the Elder)The Tower of Babel, 1563
Camp Category Thing Connections Fact Behavior InheritanceCRC Cards Class N/A Collaboration (Attribute) Responsibility Superclass/SubclassERD Entity Type Entity Relationship Attribute N/A Supertype/SubtypeRelational Relation Tuple Foreign Key Attribute N/A N/ADatabase Table Row Database Key Column Service, Procedure 3 VariationsProgrammer Layout Record Pointer Variable Function Base/DerivedUML Class Object Association Property Method Generalization/Specialization
Etc., etc., etc…Type, Structure
Occurrence, Instance
Pairing Field, ItemMessage, Operation, Algorithm, Trigger, Routine
Parent/Child, Is-a, Root/Branch/Leaf, Extension
Attribute or Entity?
Attributes Don’t have Attributes
Attributes are “OF” a class
Jean TinguelySelf-Propelled Meta-Mechanical Machine
1954
Object
An object (business object) is a thing the business needs to know about. Classes are groups (classifications) of objects.
In most discussions, “class”, “object” and “entity” can be used interchangeably.
In addition to business objects, there areinfrastructure objects. During analysis, you should only discuss business (entity) objects.
Attribute
An attribute is a piece of information about an object needed in your business.
CRUD: Create, Read, Update, Delete
An attribute or variable is a fact about an object. It can hold only one value at a time. Attributes and relationships do not have attributes; if there is a fact to be kept, it is an object in its own right, not an attribute.
Attribute (Field) Properties IDentifier (Name and Primary Key) Data Type
– Min, Max or other range– Default Value or Algorithm– Validation Rule– Select Values (Lookup)
Format– Length– Decimal Places
Required or Optional?
Marcel MarienThat which Cannot be Found, 1937
Class in UML
CLASSCLASS
Attribute1Attribute2Attribute3
Method1()Method2()UML: Unified Modeling Language
Associated with “The Three Amigos”(Spanish: “Los Tres Buddies”) Grady Booch James Rumbaugh & Ivar Jacobson
