RESO Data Dictionary FAQ

The RESO Data Dictionary is the real estate industry’s universal language for data. It empowers a wide range of systems to talk to each other in a seamless manner. The Data Dictionary provides a format for industry standard data, unique local data, international variations and language translations.

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The RESO Data Dictionary was developed to standardize data terms and structures to create efficiency in the connected digital real estate industry, which evolved from printed MLS books and proprietary legacy computer systems.

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The main components of the Data Dictionary are a tree structure of resources, fields and lookups (aka enumerations). Resources are major categories such as Property, Member (i.e., real estate agents), Office (i.e., real estate brokers) and Media (i.e., photographs, videos, virtual tours). Fields are specific data points grouped together in resources. For example, ListPrice and StandardStatus are fields within the Property Resource. Lookups are specific types of fields with options for values, such as the lookup field Fencing with lookup options for Vinyl, Wood, Wrought Iron and 26 other lookups.

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Fields are specific data points grouped together in resources. For example, ListPrice and StandardStatus are fields within the Property Resource.

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Lookups are specific types of fields with options for values, such as the lookup field Fencing with lookup values for Vinyl, Wood, Wrought Iron and 26 other lookups.

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The current Data Dictionary can be accessed via the DD 2.0 Wiki at ddwiki.reso.org. It can also be downloaded in spreadsheet format.

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Benefits include simplified integrations, faster creation of new tools, a seal of approval from RESO certification and enhanced industry innovations, competition and collaboration.

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The Data Dictionary Wiki provides detailed information on data resources, fields and lookups (aka enumerations), guiding the development of data systems. It has extensive cross-links to guide users through the connected layers of the dictionary.

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Extensibility with the Data Dictionary means data providers can create new local fields to address specific needs that are not currently covered by the Data Dictionary and still be in compliance with the standard.

Providers may extend the Data Dictionary with custom resources, fields or lookups (aka enumerations) when there is no standard option available. If the data element in question is common and not just local to a specific market, it may be added to the Data Dictionary. Contact dd@reso.org to request the addition of new items.

Omissibility allows data providers to exclude fields that are irrelevant for their business needs from their technology implementations. These features ensure that the Data Dictionary can meet the needs of diverse organizations without compromising the standardization of core data elements.

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The Data Dictionary's extensibility feature means that data providers can create new local fields to address specific needs that are not currently covered by the Data Dictionary and still be in compliance with the standard for certification.

Although providers may use their local elements, when there are standard data elements defined in the Data Dictionary for the same specific purpose, those standard elements should be provided.

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Implementation of the entire Data Dictionary is not expected or required for certification. The dictionary standard’s omissibility feature allows data providers to only use the elements relevant to their specific needs.

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RESO provides a standard for delivering multi-language metadata in the Data Dictionary, and it has been extended to other languages in several countries.

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Contributors include technologists and business leaders from MLSs, REALTOR® associations, brokerages and vendors. Proposals can be submitted to RESO staff and the Data Dictionary Workgroup at dd@reso.org.

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New fields are added to the Data Dictionary year-round and often ratified annually in new versions of the standard to support evolving industry needs.

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The Lookup Resource defines the values for lookups (enumerations) in metadata. It contains predefined lists of acceptable values for specific fields and alternative mappings for deprecated items. The Lookup Resource is not currently mandatory for certification, but it is highly recommended to ensure consistent used of standard and local data elements, facilitating smoother data exchanges.

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The Data Dictionary specification includes validation rules that are enforced to ensure that data entries meet specified criteria, such as value ranges or formats, maintaining data quality and integrity.

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The concept of “native” Data Dictionary implementations comes up frequently.

RESO has no specific guidelines for how a system or database should be implemented. RESO certification measures how data is communicated using a standard API rather than how it is represented at the database or user interface (UI) level.

In some cases, there may be advantages to using the Data Dictionary for the underlying database structure; however, it is not designed to be a database schema and there are caveats and limitations to this approach. There also may be benefits to using Data Dictionary standard names and values in the UI, since it provides consistency between what goes in and out of the system.

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The RESO Data Dictionary establishes standard names and locations for resources, fields and lookups (aka enumerations); however, different providers support different data elements and there are sometimes multiple ways to express standard data elements.

For example, there are flattened ListAgent fields in the Property Resource, but there is also a ListAgent expansion that allows end users to combine the information from the Member Resource into the ListAgent field in the Property Resource directly.

Not all providers offer expanded Member Resource information and, even if they do, data consumers might not have access to expanded Member Resource data in their feeds. Additionally, this information can change over time, whereas Member Resource information flattened into the Property Resource usually reflects information at the time of entry.

There are also cases where some providers will support YN fields on their own (HorseYN), in their corresponding feature fields (HorseAmenities) or both.

End users should be prepared to support obtaining information from different locations supported by the standard. RESO is currently working on eliminating unnecessary duplication from the Data Dictionary.

However, some “duplication” in the Data Dictionary is useful. For example, PoolPrivateYN communicates similar information to the Private lookup option of the PoolFeatures field, although they have different uses. In this case, the PoolFeatures field can provide other descriptions of the pool, in addition to it being private (e.g., In Ground, Heated). The PoolPrivateYN field can only communicate whether or not the pool is private but these types of fields can be more useful for high-level filtering by data consumers.

For questions or comments, contact dd@reso.org.

See the DD Wiki for more info on fields described when discussing Differences in Data Dictionary Implementations.