There is currently no published schema available for the  App Broker database.  The following is an overview of some of the most commonly referenced tables.  These are often queried for reporting and troubleshooting purposes:

• WD_AppSettings – Stores the majority of the settings from the Admin tab
• WD_PackageRequests – used to store the data for requests that have been submitted. Likely the most referenced table.
• WD_WebPackages – Used to store information about catalog items that have been created.
• WD_SiteToAdvert – Used to store information about mappings between catalog items and SCCM collections/advertisements.
• WD_ApprovalProcess – Used to store approvers' mappings for requests that have been submitted. In general, the WD_ApprovalXXX tables store information about approvals.. Some of these are difficult to decipher.
• WD_ApproverStatus – Stores alternate approver mappings and whether or not an approver is out of office.
• WD_Actions – Stores mappings of actions to catalog items and the “events” which trigger them (on submit, on fail, etc.).
• WD_WebPackages – Stores web service actions that have been created. Referenced by WD_Actions.
• WD_Profile – Contains information about users and their associated user GUID from AD
• WD_Localizations – Stores localized strings (including English)
• WD_Notifications – Stores notification text(email)
• WD_Languages – Stores languages that are currently enabled.
• WD_ITSM_XXX – Stores information about ITSM actions (Remedy, ServiceNow)
• WD_MailQueue - Stores information about notifications that have been sent and need to be sent. Older data is purged automatically to prevent the table from growing too large.
• WD_ErrorLog – Stores errors. Same information as is typically written to log files.
• WD_MyAppsAlert – Stores information about alerts which have been created by MyApps.. This is a necessity for debugging many My Apps issues.
• WD_Question – Stores information about questions that have been created.
• WD_ResponseQuestionAuditTrail – Stores answers to questions in addition to changes to answers.
• WD_RequestTarget- Stores the “target” user/device for a request. Tied to WD_PackageRequests table.
• WD_NodeSecurity – Stores Admin permissions for users accessing the site. Generally, only referenced when there is a problem. A typical problem would consist of a “bad” GUID being stored in the table. See the ValidateSecurityGUIDs.asmx web service to help identify.
• WD_CatalogSecurity – Stores catalog permissions.
  
  Sync related tables – Populated during the nightly data sync from SCCM discovery data.
• WD_User – Users imported from SCCM
• WD_Computer – Computers imported from SCCM
• WD_UserComputerMap – mappings between users and computers imported from SCCM.

In most cases, the built-in reports  (those available under the Reporting tab) in App Broker will reference many of the above tables. The queries used by the built-in reports are actually stored in an XML file named AdminStudio.Reports.xml. This file can be found in the web/ReportDefinition folder under the App Broker install directory. The queries in this file can be a handy reference for those looking to create their own custom queries and reports.