Data Dictionary Purpose

  1. Serve as a common center for expressions of fields and lookups (enumerations) found in a RESO-certified data source.

  2. Act as a universal guideline for the fields and lookups found in Multiple Listing Service (MLS) listing input modules.

As RESO standards have grown, a common ground for fields and enumerations has been established. Keeping a centralized method of expressing property and listing concepts will mitigate implementation errors, ease field mapping and foster innovation around a more stable and cost-effective center. These benefits can be achieved by implementing the RESO Data Dictionary into services.

Through this international data standard, technological interoperability for real estate services and input forms is achievable. As real estate listings move from local systems to IDX, VOW and other approved systems, the Data Dictionary helps to ensure that the meaning of the data is not diluted or misinterpreted. When MLS subscribers see the same names and terminology around the data in external services, it creates consistency for both subscribers and their clients that see MLS reports and displays.

Wiki Tree Structure

The Data Dictionary Wiki is built on a tree structure with a traditional expandable/collapsible tree paradigm in the left navigation panel.

  • The highest level is devoted to major categories, mostly known as resources. Terms like Property, Member (i.e., real estate agents), Office (i.e., real estate brokers) and Media will be found here.

  • The second level often shows as the group level, further refining a selection process from the parent node.

  • Lower levels contain the actual Data Dictionary fields.

  • Lookups (also known as enumerations) are structured somewhat differently but should be obvious.

There are extensive links and cross links within the Data Dictionary wiki. For example, while viewing a field with lookups, you can also expand lookup details. It is also possible to chain backwards from any lookup items to one of its referenced fields.


The RESO Data Dictionary is designed to grow with the real estate industry. New ideas are welcome. Change ideas require the following accompanying information:

  • Name: Review existing fields or enumerations and create a name that fits the current convention.

  • Definition: Write a robust definition of your entry idea.

  • Data Type: Include your recommended data type and maximum field length.

  • Lookups/Enumerations: Include enumerations if your recommended field is a picklist. Enumerations will also need a robust definition.

  • Justification: Offer a meaningful reason that the field is important to your market. If the field has legal or MLS rules requirements, include a reference back to the law or rules in question.

  • Utilization: Include an indication of how frequently your field or enumeration is used as a count of total listings using the field or enumeration and the number of listings in your sample. From this, a percentage of utilization will be created. Include the criteria used to determine the sample of listings used.

  • Duplication: Review the Data Dictionary thoroughly to ensure that the new idea is not duplicating an existing field or enumeration. Rather than adding additional fields or enumerations, alternate names can be added to the Synonym column and/or used to improve a field's definition.

Thank you for your interest and participation in the RESO Data Dictionary. All MLSs are invited to refer to the Data Dictionary as a future center for their own metadata (field/enumeration) change decisions.

Please send questions and/or suggestions to RESO at If you want to be part of the real estate data conversation, please join our growing ranks as a RESO member. Membership includes free certification.

Page Revision Date: Mar 21 2021 17:46