Analysis schemas are built by publishing them to the Pentaho Server. Each schema is validated to make sure that there are no errors before it is built; if there are any, they'll be shown to you and the schema will fail to publish. If you want to see the errors marked in Schema Workbench before you publish, go to the Options menu and select Require Schema. When this option is checked, schema validation will happen as new elements are added, and any errors will show as a Red X next to the offending element.