The Physical Data Model - Microsoft SQL Server 2008 Analysis Services - page 359

Washington (1) Level State

Seattle (1) Kirkland (2)

Level City

Irina (1) Sasha (2) Py (3) Edward (4)

Level Customer

Level State Level City Level Customer

Irina

1 1

Sasha

1 1

Py

1 1

Edward

1 2

FIGURE 20.10

Analysis Services builds the path to the member by enumerating the DataIDs

of its ancestors.

Analysis Services uses the decoding table on different phases of server work (for
example, when processing cubes, building indexes, building aggregations, executing
queries, and performing other operations). Performance of the server depends heavily on
the performance of the decoding operation, especially when decoding is carried out
during query execution.

A decoding table is a compressed store, kept in a file named <level ID>.dstore , where
<level ID> represents the identifier of the level. The structure of the decoding table is
almost the same as the structure of the set store for a level. Similar to the structure of the
hierarchy, a decoding table contains columns with the DataID s of the member's ancestors.
However, a number of differences exist between the decoding table and set store of the
level:

Records in a decoding table are ordered not by level index, but by DataID . Therefore,
the decoding table uses the same order as the keys of the attribute that defines the
level.

.

. There is no need to store the DataID of the member because it's already known by

the ordinal of the record (which is the DataID of the member) in the decoding table.
Therefore, the decoding table contains only the DataID values of ancestors for the
current member.

. The decoding table is built for the levels of native hierarchies. For more information

about native hierarchies, see Chapter 7, “Measures and Multidimensional Analysis.”