# Multidimensional Expression Language The Multidimensional Expression Language (MDX) is an OLAP database query and calculation language similar to SQL. It is the method by which a dataset is retrieved from a OLAP database. While you do not necessarily have to know MDX in order to use Pentaho's client tools, you should be somewhat familiar with it for the purpose testing your Mondrian schema. --- # 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.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.