An expression is any combination of operators, constants, functions, and other components that evaluates to a single value. You build expressions to create calculation and filter definitions. A calculation is an expression that you use to create a new value from existing values contained within a data item. A filter is an expression that you use to retrieve a specific subset of records.

The expression editor shows the expression components that are supported by the data source in which the metadata is stored. For example, if you import metadata from an Oracle data source, the expression editor shows only the elements that are supported in Oracle.

If you are using a DB2 data source, note that the subtract operator is invalid if you combine the datatypes timestamp2 and packed decimal.

When creating an expression that will be used in a double-byte environment, such as Japanese, the only special characters that will work are ASCII-7 and ~ -- || - $ ¢ £ ¬.

Quality of Service Indicators

Not all data sources support functions the same way. The data modeler can set a quality of service indicator on functions to give a visual clue about the behavior of the functions. Report authors can use the quality of service indicators to determine which functions to use in a report. The quality of service indicators are:

• not available (X)

  This function is not available for any data source in the package.

• limited availability (!!)

  The function is not available for some data sources in the package.

• poor performance (!)

  The function is available for all data sources in the package but may have poor performance in some data sources.

• unconstrained (no symbol)

  The function is available for all data sources.

SAP BW Support

SAP BW does not support all operators or summaries. This can be confusing if you have imported SAP BW metadata and non-SAP BW metadata into the same model.

SAP BW does not support the following operators:

• like

• lookup

SAP BW does not support the following member summaries:

• date-time

• interval

• interval month

• interval day

• interval day to hour

• interval day to minute

• interval day to second

• interval hour

• interval hour to minute

• interval hour to second

• interval minute

• interval minute to second

• interval second

• interval year

• interval year to month

• moving

• running

• time with time zone

• timestamp with time zone

Cell values are date, number, or time. Attribute values are strings.