# Dimension A dimension is a collection of hierarchies. There are two kinds: a public dimension belongs to a schema, and be used by several cubes; a private dimension belongs to a cube. The `foreignKey` field is only applicable to private dimensions. --- # 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/dimension.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.