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The Slowly Changing Dimension transformation provides the
following functionality for
managing slowly changing dimensions:
Matching incoming rows with rows in the lookup table to identify
new and existing rows.
Identifying incoming rows that contain changes when changes are
not permitted.
Identifying inferred member records that require updating.
Identifying incoming rows that contain historical changes that
require insertion of new
records and the updating of expired records.
Detecting incoming rows that contain changes that require the
updating of existingrecords, including expired ones.
The Slowly Changing Dimension transformation supports four types
of changes: changing
attribute, historical attribute, fixed attribute, and inferred
member.
Changing attribute changes overwrite existing records. This kind
of change is equivalent
to a Type 1 change. The Slowly Changing Dimension transformation
directs these rowsto an output named Changing Attributes Updates
Output.
Historical attribute changes create new records instead of
updating existing ones. The
only change that is permitted in an existing record is an update
to a column that indicateswhether the record is current or expired.
This kind of change is equivalent to a Type 2
change. The Slowly Changing Dimension transformation directs
these rows to two
outputs: Historical Attribute Inserts Output and New Output.
Fixed attribute changes indicate the column value must not
change. The Slowly Changing
Dimension transformation detects changes and can direct the rows
with changes to an
output named Fixed Attribute Output.
Inferred member indicates that the row is an inferred member
record in the dimensiontable. An inferred member exists when a fact
table references a dimension member that is
not yet loaded. A minimal inferred-member record is created in
anticipation of relevant
dimension data, which is provided in a subsequent loading of the
dimension data. TheSlowly Changing Dimension transformation directs
these rows to an output named
Inferred Member Updates. When data for the inferred member is
loaded, you can update
the existing record rather than create a new one.
Note
The Slowly Changing Dimension transformation does not support
Type 3 changes, which requirechanges to the dimension table. By
identifying columns with the fixed attribute update type, you
can capture the data values that are candidates for Type 3
changes.
At run time, the Slowly Changing Dimension transformation first
tries to match the incomingrow to a record in the lookup table. If
no match is found, the incoming row is a new record;
therefore, the Slowly Changing Dimension transformation performs
no additional work, and
directs the row to New Output.
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If a match is found, the Slowly Changing Dimension
transformation detects whether the row
contains changes. If the row contains changes, the Slowly
Changing Dimension transformation
identifies the update type for each column and directs the row
to the Changing AttributesUpdates Output, Fixed Attribute Output,
Historical Attributes Inserts Output, or Inferred
Member Updates Output. If the row is unchanged, the Slowly
Changing Dimension
transformation directs the row to the Unchanged Output.
Slowly Changing Dimension Transformation Outputs
The Slowly Changing Dimension transformation has one input and
up to six outputs. An output
directs a row to the subset of the data flow that corresponds to
the update and the insert
requirements of the row. This transformation does not support an
error output.
The following table describes the transformation outputs and the
requirements of their
subsequent data flows. The requirements describe the data flow
that the Slowly Changing
Dimension Wizard creates.
Output Description Data flow requirements
ChangingAttributes
Updates
Output
The record in the lookup table
is updated. This output is used
for changing attribute rows.
An OLE DB Command transformation updates the
record using an UPDATE statement.
Fixed
Attribute
Output
The values in rows that must
not change do not match
values in the lookup table.
This output is used for fixedattribute rows.
No default data flow is created. If the
transformation is configured to continue after it
encounters changes to fixed attribute columns, youshould create
a data flow that captures these rows.
Historical
Attributes
Inserts Output
The lookup table contains at
least one matching row. Therow marked as current must
now be marked as "expired".
This output is used forhistorical attribute rows.
Derived Column transformations create columnsfor the expired row
and the current row indicators.An OLE DB Command transformation
updates the
record that must now be marked as "expired". The
row with the new column values is directed to the
New Output, where the row is inserted and markedas
"current".
Inferred
MemberUpdates
Output
Rows for inferred dimension
members are inserted. Thisoutput is used for inferred
member rows.
An OLE DB Command transformation updates therecord using an SQL
UPDATE statement.
New Output
The lookup table contains nomatching rows. The row is
added to the dimension table.
This output is used for new
rows and changes to historicalattributes rows.
A Derived Column transformation sets the current
row indicator, and an OLE DB destination inserts
the row.
Unchanged
Output
The values in the lookup table
match the row values. This
No default data flow is created because the Slowly
Changing Dimension transformation performs no
