Databases Reference
In-Depth Information
This definition contains neither a definition of multidimensional space nor a dimension
hierarchy. If we want to define a multidimensional space, we must use a collection of
attributes to define the coordinates of that space. In the next section, we look at the
attribute collection for our sample
Customer
dimension.
Dimension Attributes
The multidimensional model contains a collection of attributes that defines a set of
“domains” of a dimension's data; one domain is a dimension attribute. We use the term
domain
as it defined in the relational database theory: a limited list of values (scalars).
However, implementations of relational databases essentially ignore this definition. In
practice, implementations of the relational data model manipulate columns that will
accept any value (of the appropriate type).
In the multidimensional model,
attribute
defines domain—a list of the same type values,
which we call key values. All key values of attribute have the same data type. Key is a
unique identifier of a dimension member. (For the definition of a dimension member, see
Chapter 2, “Multidimensional Space.”) For each unique key value, there is a unique
dimension member. The difference between the implementation of a domain in the rela-
tional and multidimensional data models is shown in Figure 5.1.
Relational Model
Multidimensional Model
Column = “Domain”
Attribute = “Domain”
Column 1
Column 2
Column 3
Key
Name
Translation
Property
Irina
Alexander
Edward
.....
Value N
Gorbach
Berger
Melomed
.....
Value N
F
M
M
.....
Value N
01
02
03
.....
Value N
Gorbach
Berger
Melomed
.....
String N
Gorbach
Berger
Melomed
.....
String N
F
M
M
.....
Value N
FIGURE 5.1
The implementation of a “domain” differs between the relational and the multidi-
mensional models.
As shown in a Figure 5.1, an attribute is an analog of a column in the relational imple-
mentation of the domain. However, in addition to the scalar values, the multidimensional
Search WWH ::
Custom Search