2. MetaData “Data about Data” College of Alameda pmcdermott@peralta.edu 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

3. One cannot give what one does not have One cannot have what one has no place to keep Nēmō dat qua nōn habet.

4. The Sour of Babel Illustrates the Metadata obstacle to the Semantic Web: We need to call the Same thing by the Same name, Different things by Different names Pietr Brueg(h)el (the Elder) The Tower of Babel, 1563

5. Attribute or Entity? Jean Tinguely Self-Propelled Meta-Mechanical Machine 1954

6. 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 are infrastructure objects. During analysis, you should only discuss business (entity) objects.

7. 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.

8. 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 Marien That which Cannot be Found, 1937

9. Class in UML CLASS Attribute1 Attribute2 Attribute3 Method1() Method2() Associated with “The Three Amigos” (Spanish: “Los Tres Buddies”) Grady Booch James Rumbaugh & Ivar Jacobson