# Attributes | Attribute | Data Type | Definition | | ----------- | --------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | source | String | Name of the source dimension. Must be a dimension in this schema. Case-sensitive. | | level | String | Name of the level to join to. If not specified, joins to the lowest level of the dimension. | | usagePrefix | String | If present, then this is prepended to the Dimension column names during the building of collapse dimension aggregates allowing 1) different dimension usages to be disambiguated during aggregate table recognition and 2) multiple shared dimensions that have common column names to be disambiguated. | --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.pentaho.com/install/9.3-install/multidimensional-data-modeling-in-pentaho/about-multidimensional-expression-language/mondrian-schema-element-reference/dimensionusage/attributes.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.