By Saul Klein
For decades, real estate data was local, fragmented, and inconsistent. Each Multiple Listing Service (MLS) had its own rules, field names, and data formats. What one MLS called Beds, another called Bedrooms, and another labeled BR. Even something as basic as a price or property type could be stored differently from market to market.
This worked when brokers stayed local, but once real estate went digital in the 1990s, that fragmentation became a serious problem. National portals, CRMs, and analytics tools couldn’t easily combine data from different MLSs. The industry desperately needed a common language.
The First Attempt: RIN and DxM
In the mid-1990s, before RETS or RESO, the National Association of REALTORS® (NAR) launched an ambitious project called RIN — the REALTORS® Information Network. RIN was one of NAR’s earliest attempts to bring real estate online — a kind of digital marketplace and technology platform for MLSs and brokers.
Out of that effort came something ahead of its time: the Data Exchange Method (DxM).
DxM was an early attempt at a Data Dictionary — a system that defined consistent names and structures for real estate data. It was designed to make it easier for MLSs and vendors to exchange property information electronically.
Unfortunately, technology and connectivity were still limited at the time. Internet speeds were slow, software was expensive, and few MLSs were ready to make large-scale digital transformations. DxM’s ideas were sound, but the industry wasn’t yet ready to implement them widely.
Still, DxM laid the intellectual foundation for what would come later — proving that standardizing data was possible and valuable.
The Next Step: RETS Brings Structure
By the late 1990s, as the internet matured, NAR and industry leaders revisited the challenge. In 1999, they introduced the Real Estate Transaction Standard (RETS) — the first practical, nationwide framework for moving real estate data between systems.
RETS was revolutionary. It allowed MLSs to share listing data with brokerages, vendors, and national portals using a consistent, machine-readable format. For the first time, companies could pull property listings from multiple MLSs without reinventing the wheel each time.
But RETS had limits. It was designed for an earlier web era — before mobile apps, APIs, and cloud computing. It required complex setup and ongoing maintenance. As the industry became more digital, it needed something faster, lighter, and easier for developers to use.
The Birth of RESO: A Modern, Open Standard
In 2011, NAR’s standards work evolved into a new, independent nonprofit: the Real Estate Standards Organization (RESO). RESO’s mission was to finish what RIN, DxM, and RETS had started — to create simple, universal, and modern standards for real estate data in the digital age.
Today, RESO provides the framework that powers how MLS data moves throughout the real estate industry.
What RESO Does
RESO maintains and updates a set of open standards that make real estate systems compatible with one another. The key components are:
- The Data Dictionary:
A complete glossary and rulebook for real estate data — defining how every field is named and used. For example, “ListPrice,” “BathroomsFull,” and “AgentEmail” now mean the same thing everywhere. - The RESO Web API:
A modern, secure, and developer-friendly way to exchange data. It’s based on the same REST and OData technologies used by major internet platforms. This replaced the older RETS framework and dramatically reduced the complexity of integrations. - The Universal Property Identifier (UPI):
A unique digital ID for every property — like a VIN number for real estate. The UPI is still in early adoption but promises to unify listings, tax records, and property histories under one consistent identifier.
Together, these tools allow real estate systems to share data seamlessly — creating an ecosystem that’s faster, cheaper, and far more reliable than ever before.
Why Standards Matter
Before standards, every new integration between MLSs and software vendors required expensive, custom engineering. With RESO’s framework, those translation costs are largely eliminated. Developers can now write once, use anywhere, allowing innovation to spread faster across markets.
The benefits ripple through the industry:
– MLSs can partner and share data more easily.
– Brokerages and agents get faster, more reliable technology.
– Consumers see cleaner, more accurate listings.
– Vendors can build tools that work nationally instead of market-by-market.
Standards have become the backbone of trust and innovation in real estate technology.
Why Full Adoption Takes Time
Even with RESO’s success, complete standardization remains a work in progress.
– Legacy systems still rely on old RETS feeds.
– Partial adoption — some MLSs are RESO-certified but haven’t yet migrated all data fields.
– Local customization — markets often keep regional fields that don’t exist in the core standard.
– Resource gaps — smaller organizations may lack funding or technical support to fully implement.
Still, the momentum is strong. Over 90% of MLSs in the U.S. have been certified on RESO’s standards, and international interest continues to grow rapidly as more global organizations explore aligning with RESO.
Forces Driving Full Adoption
– NAR mandates and policy pressure have set minimum compliance levels for U.S. MLSs.
– Certification programs and public leaderboards create accountability and transparency.
– Vendor demand — tech companies prefer standardized data because it lowers integration costs.
– Education and training — RESO’s courses and working groups help organizations modernize.
– Global interest — as real estate technology becomes more international, other markets are showing growing curiosity and engagement with RESO’s approach to data consistency.
From DxM to RESO: A 30-Year Journey
When RIN introduced the Data Exchange Method (DxM) nearly 30 years ago, it was a glimpse into the future — a world where all real estate data could move effortlessly between systems.
It took decades of evolution — through RETS and into RESO — to make that vision a reality. Today, RESO’s standards are turning what was once an industry of digital islands into an interconnected network.
The story of DxM, RETS, and RESO is the story of real estate learning to speak the same language — a transformation that continues to shape how homes are listed, found, and sold across the world.
About the Author:
Saul Klein was a member of the first team at the REALTORS® Information Network and was instrumental in the movement of the real estate industry into the digital age.
