CDE基本概念

Customer

，但一个

Customer

可以有任意多个

Order

。

下面这个表给出了最普遍的多样性示例。

每个类图包括类，关联和多样性表示。方向性和角色是为了使 图示得更清楚时可选的项目。

CDE

基本概念

The

fundamental

information

component

in

the

ISO/IEC

11179

model

is

the

data

element

,which constitutes a single

（单个）

unit of data considered indivisible

（不可分割的）

in

the context in which it is used. Another way of saying this is that a data element is the smallest

unit of information that can be exchanged in a transaction between cooperating systems.

A critical notion

（概念）

in the metadata model is that any concept represented by a data

element

must

have

an

explicit

（明确的）

definition

that

is

independent

of

any

particular

representation.

In

order

to

achieve

this

in

the

model,

the

ISO/IEC

11179

standard

specifies

the

following four components:

1. A

DataElementConcept

consists of an

object

and a selected

property

of that object;

2. The

ConceptualDomain

is the set of all intended meanings for the possible values of an

associated DataElementConcepts;

3. The

V

alueDomain

is a set of accepted representations for these meanings;and

4. A

DataElement

is a combination of a selected DataElementConcept and a ValueDomain.

A simple example should help to clarify these definitions. Figure 3.1-1 shows a DataElement

that

might

be

used

to

represent

hair

color.

The

associated

DataElementConcept

use

the

ObjectClass

Hair

and the Property

Color

to define the intended concept. The intended meanings

for this data element are the familiar hair colors blonde,brunette,etc.,but the ValueDomain uses a

numeric representation that is mapped to these intended meanings. Both the DataElementConcept

and

the

ValueDomain

are

components

of

the

DataElement

，

and

each

references

the

same

ConceptualDomain, which is defined outside the DataElement. Important principles of this design

are:

?

The DataElementConcept is used to signify a concept

independent of representation.

?

The ValueDomain specifies a set of representational values

independent of meaning.

?

The DataElement combines a specific object and property with a value representation.

?

The

ConceptualDomain

specifies

the

complete

set

of

value

meanings

for

the

concept

and allows the interpretation of the representation.

Figure 3.1-2 uses a UML Class diagram to show the cardinality constraints that hold for these

relations. Each DataElement must specify exactly one DataElementConcept and one V

alueDomain

in order to fully specify the data element. Similarly, each DataElementConcept and ValueDomain

must specify exactly one ConceptualDomain. Conversely, a ConceptualDomain may be associated

with any number of ValueDomains and any number of DataElementConcepts. Figure 3.1-3 shows

an

example

of

this,

using

the

color

property

of

different

geometric

objects

as

DataElementConcepts, and alternate color representations for the ValueDomains.