Compendium

Real-Estate / MLS / Property Data DSLs Family Index

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Real-Estate / MLS / Property Data DSLs Family Index

type: language-family-index family: real-estate-property languages_catalogued: 26 tags: [language-reference, family-index, real-estate-property, reso, rets, mismo, oscre, trid, alta, mls, land-registry]

Real-Estate / MLS / Property Data — Family Index

Family overview

Real-estate property-data languages are the family of schemas, dictionaries, and transport protocols that describe listings, transactions, appraisals, closings, and registered property data. Unlike financial-regulatory mortgage schemas (see financial-regulatory) or building-information modelling languages (see construction-bim), this layer is dominated by a single organisation in the US — the Real Estate Standards Organization (RESO) — and a thick tail of regional MLS systems, title/closing standards, commercial-real-estate (CRE) data models, and national land registries. RESO defines two complementary artefacts: the Data Dictionary (the canonical vocabulary of ~2,500 listing fields, lookup enumerations, and resources, currently DD 2.0; DD 1.7 URLs are scheduled to be disabled 23 March 2026) and the Web API (a REST + OData v4.01 transport that superseded the older RETS XML feed). Over 500 MLSs and ~90% of US MLS subscribers are now served by RESO-certified Web API services.

The big migration story in this family is RETS → RESO Web API. RETS (Real Estate Transaction Standard) was an XML-over-HTTP feed standard first published in 1999 and deprecated by RESO in June 2018. The Web API (REST/JSON/OData) replaced it but the long tail of legacy integrations has dragged on for nearly a decade — converted feeds covered ~62% of US subscribers by 2024 per RESO’s transition leaderboard, with the remainder still on RETS into 2026. On top of the Web API sit two newer RESO standards: RESO Common Format (an API-agnostic JSON payload format that lets non-MLS participants — appraisers, photographers, tour-providers — exchange Data-Dictionary-aligned data outside the OData transport) and RESO Payloads (pre-defined payload subsets — IDX, VOW, BBO — to constrain what data flows where). Aggregators Trestle (Cotality, formerly CoreLogic) and MLS Grid sit on top of the Web API, normalising 100+ MLS feeds into a single subscription; Trestle announced full DD 2.0 certification in 2025 and is migrating its API URL host before end-of-2025.

The closing/title/settlement layer is governed by a different set of standards bodies. ALTA (American Land Title Association) publishes the Best Practices framework (current v4.2, published August 2025, adding identity-verification and BEC controls under Pillar IV) and the ALTA Settlement Statement forms. The TILA-RESPA Integrated Disclosure (TRID) rule, administered by the CFPB since 2015, defines the Loan Estimate and Closing Disclosure forms that bridge mortgage and title data — amended December 2024 with model forms for residential PACE transactions. MISMO XML and ULDD (financial-regulatory) describe the underlying loan and securitisation data; PRIA (Property Records Industry Association) eRecording standards (v2.4.2 and v3.0 XML schemas) define how recorded documents flow into county recorders’ offices.

Commercial real estate is a parallel universe. OSCRE (Open Standards Consortium for Real Estate) maintains the Industry Data Model (IDM) — open-access since early-2025, with a “smart data highway” vision announced February 2026 that adds semantic relationship layers on top of the traditional data dictionary. CRE property-management platforms Yardi, MRI Software, and RealPage all expose proprietary data-exchange formats — Yardi via the Standard Interface Partnership Program (SIPP, ~450 partners), MRI via the MRI Information eXchange (MIX) open-API platform. Commercial data aggregators CoStar, LoopNet, and ATTOM publish their own proprietary feeds. The international tail — UK HM Land Registry (transitioning SOAP→REST APIs and targeting complete digitisation of England & Wales by 2030), OS MasterMap (Ordnance Survey’s geospatial property base), and various eRegistration systems in Ireland, Australia, and elsewhere — adds national-fragmentation complexity that has no near-term harmonisation roadmap.

In our deep library

None catalogued. Real-estate / MLS / property-data DSLs do not have standalone deep-library notes; they are all XML/JSON schemas, OData services, or PDF-form definitions sitting on top of host transports.

Cross-reference:

  • financial-regulatory — MISMO + ULDD mortgage-securitisation sibling; cross-listed below where the loan/closing data flow crosses the title/property line.
  • construction-bim — BIM/IFC building-modelling sibling; OSCRE’s IDM overlaps at the asset-equipment vocabulary boundary but is operations-side, not design-side.
  • api-description — RESO Web API is OData v4.01, which is itself described via CSDL/EDMX schemas plus OpenAPI bindings.
  • geospatial — GeoMLS, Spatial RESO, and OS MasterMap intersect with GIS formats catalogued in the geospatial family.
  • citation-formats — county-recorded document references and title-chain citations share lineage patterns with bibliographic-citation conventions.
  • notation-spec — RESO and OSCRE both express their vocabularies through formally-defined data models (XSD historically, JSON-Schema + OData CSDL now).
  • identity-auth-policy — RESO Web API authenticates via OAuth2 (Bearer tokens, RFC 6749/6750); ALTA Best Practices 4.2 added identity-verification requirements that touch this family from the policy side.

Tier 3 family table — Residential MLS / RESO

FormatFirst appearedOriginTypeStatus (2026)URL
RESO Data Dictionary2011 (DD 1.0); current 2.0Real Estate Standards OrganizationXSD-/JSON-Schema-described property data vocabulary (~2,500 fields)Active — DD 2.0 is the current cert baseline; DD 1.7 URL endpoints scheduled to be disabled 23 March 2026https://www.reso.org/data-dictionary/
RESO Web API2014 (cert program); current Web API Core 2.xReal Estate Standards OrganizationREST + OData v4.0/4.01 transport, JSON payloads, OAuth2Active — successor to RETS; ~90% of US MLSs certifiedhttps://www.reso.org/reso-web-api/
RETS (Real Estate Transaction Standard)1999 (RETS 1.0); RETS 1.8 final (2009)NAR / RESOXML over HTTP login/search/getobject; binary metadata responsesDeprecated since June 2018, but still widely deployed in legacy feeds covering ~38% of US subscribers per the RESO Transition Leaderboard (2024)https://www.nar.realtor/real-estate-transaction-standards-rets
RESO Common Format (RCF)2022 (initial proposal); 2024 productionRESO Transport WorkgroupAPI-agnostic JSON payload format aligned with Data Dictionary via @reso.contextActive, growing — used for non-MLS payloads (appraisal, showings, tours, photography) and webhook/S3 deliveryhttps://www.reso.org/reso-common-format/
RESO Payloads (IDX/VOW/BBO)2018+RESOPre-defined Data-Dictionary subsets for IDX, VOW, Broker-to-Broker exchangeActive, defines what data flows where under the post-NAR-settlement ruleshttps://www.reso.org/payloads/
Trestle (Cotality / CoreLogic)2017CoreLogic (now Cotality)Proprietary RESO Web API + RETS aggregator over 100+ MLSs; DD 2.0 certified 2025Active; API host migration completing end-2025https://trestle-documentation.corelogic.com/
MLS Grid2018MLS Grid (industry consortium)Single RESO-compliant feed across participating MLSs; one licence, one rulesetActive, growing — direct alternative to Trestlehttps://www.mlsgrid.com/
Bridge Interactive API (Spark Platform)2016Bridge Interactive (Zillow Group)RESO Web API aggregator; Spark Platform JSON/OData over Bridge feedsActive (Spark Platform)https://sparkplatform.com/docs/reso/overview
CRMLS / Bright MLS / NorthstarMLS / FlexMLS regional extensionsvarious (1990s+)Regional MLS organisationsLocal Data-Dictionary fields layered on RESO Web API or RETSActive, fragmented — ~600 regional MLSs each with vendor-specific extensionshttps://www.reso.org/web-api-examples/
GeoMLS / Spatial RESO2019+RESO (Spatial Workgroup)Geospatial extensions to the Web API — geometry filters, polygon search via OData spatial functionsActive, nichehttps://transport.reso.org/proposals/web-api-core.html
Schema.org RealEstateListing / SingleFamilyResidence2014 (Place types); RealEstateListing 2020Schema.org / W3C communityLinked-data vocabulary embedded in HTML via JSON-LD/Microdata/RDFaActive, used for SEO; minor compared to RESO for transactional datahttps://schema.org/RealEstateListing

Tier 3 family table — Closing / title / settlement

FormatFirst appearedOriginTypeStatus (2026)URL
ALTA Best Practices2013 (v1.0); current v4.2 (Aug 2025)American Land Title AssociationFramework document + assessment workbook for title/escrow operational controlsActive — v4.2 added identity verification, BEC defences, signing-agent controls under Pillar IVhttps://www.alta.org/policies-and-standards/best-practices/
ALTA Settlement Statement2015 (concurrent with TRID)ALTAForm definitions for buyer/seller/combined settlement statementsActive, the de facto post-TRID settlement formhttps://www.alta.org/policies-and-standards/
TILA-RESPA Integrated Disclosure (TRID)2015 (rule effective Oct 2015)CFPBFederal rule defining Loan Estimate + Closing Disclosure forms; amended Dec 2024 for PACEActive, mandatory for most US residential mortgage closingshttps://www.consumerfinance.gov/compliance/compliance-resources/mortgage-resources/tila-respa-integrated-disclosures/
MISMO XML (Mortgage)1999 (v1.x); current v3.4+MISMO (Mortgage Industry Standards Maintenance Organization)XML schemas spanning loan origination, servicing, closing, securitisation; cross-listed with financial-regulatoryActive, the canonical mortgage-side schema bridging into title/closing datahttps://www.mismo.org/standards-and-resources
ULDD (Uniform Loan Delivery Dataset)2010 (Phase 1); current Phase 4Fannie Mae / Freddie Mac / MISMOMISMO 3.0-based dataset for loan deliveries to GSEs; cross-listed with financial-regulatoryActive, mandatory for GSE loan deliverieshttps://singlefamily.fanniemae.com/delivering/uniform-mortgage-data-program/uniform-loan-delivery-dataset
Closing Insight (RamQuest, others)2014RamQuest + ALTA collaborationClosing/escrow data exchange between lenders and title agents over MISMO-aligned envelopesActive, vendor-specifichttps://ramquest.com/
PRIA eRecording XML2003 (v1.x); current v2.4.2 + v3.0Property Records Industry AssociationXML schemas + iGuide for electronic recording of deeds, mortgages, releases at county recordersActive, baseline for most US county eRecording portalshttps://www.pria.us/i4a/pages/index.cfm?pageID=3323

Tier 3 family table — Commercial real estate

FormatFirst appearedOriginTypeStatus (2026)URL
OSCRE Industry Data Model (IDM)2004 (v1); current IDM (continuously versioned)Open Standards Consortium for Real EstateOpen-access XML/JSON data model for CRE: assets, leases, transactions, occupancy, ESG, energyActive — open-source as of early 2025; “Smart Data Highway” semantic-relationship layer announced Feb 2026https://www.oscre.org/idm
Yardi SIPP (Standard Interface Partnership Program)~2005Yardi SystemsProprietary integration program with ~450 partners; Yardi Voyager native modules + REST/SOAP endpointsActive, dominant CRE property management ecosystemhttps://www.yardi.com/
MRI MIX (MRI Information eXchange)~2012MRI SoftwareOpen-API integration platform connecting ~150 third-party appsActive, the open-architecture counterweight to Yardi’s SIPPhttps://www.mrisoftware.com/
RealPage Open API~2015RealPage (Thoma Bravo)REST APIs over multifamily property management dataActive, multifamily-focusedhttps://www.realpage.com/
CoStar / LoopNet feeds1987 (CoStar)CoStar GroupProprietary CRE listing + market data feeds (REST + bulk)Active, dominant commercial-listing data sourcehttps://www.costar.com/
ATTOM Data Solutions2007 (RealtyTrac → ATTOM)ATTOM Data SolutionsProprietary nationwide property + tax + foreclosure data API (REST/JSON)Active, the commercial data-aggregator counterpart to residential MLS feedshttps://www.attomdata.com/
Zillow / Redfin / Realtor.com data feeds2006+ (Zillow founded)Zillow Group / Redfin / Move Inc. (Realtor.com)Proprietary listing + Zestimate/Redfin Estimate APIs; Bridge Interactive (Zillow) operates the Spark PlatformActive, consumer-facing portals; data flows in via MLS Grid / Trestle / Bridgehttps://www.zillowgroup.com/

Tier 3 family table — Property tax / public records

FormatFirst appearedOriginTypeStatus (2026)URL
CAMA (Computer-Assisted Mass Appraisal)1970sIAAO (International Association of Assessing Officers)Family of assessor-jurisdiction data formats; XML and proprietaryActive, fragmented by state/countyhttps://www.iaao.org/
PropertyDocs (US county recorded documents)2010sCounty recorder community + PRIASubset of PRIA eRecording XML covering deeds, mortgages, satisfactionsActive, mostly under PRIA v2.4.2/v3.0 umbrellahttps://www.pria.us/
NAREIT / REIT Watch1960 (NAREIT founded)Nareit (industry trade association)Aggregated REIT performance + holdings reporting; proprietaryActive, reference data for public REITshttps://www.reit.com/

Tier 3 family table — National (non-US) land / property registries

FormatFirst appearedOriginTypeStatus (2026)URL
UK HM Land Registry APIs2018+ (Business Gateway); REST APIs 2022+HM Land Registry (UK Govt)Catalogue of 15 APIs covering title, charges, INSPIRE polygons, price-paid data; SOAP→REST migration ongoingActive, targeting complete digital registration of England & Wales by 2030https://www.api.gov.uk/hmlr/
OS MasterMap (Ordnance Survey)2001Ordnance Survey (UK Govt)UK national geospatial property base — Topography, Address, Highways, Greenspace layers; GML/GeoPackageActive, the UK base layer for property data; ties into geospatialhttps://www.ordnancesurvey.co.uk/products/os-mastermap-topography-layer
Ireland Property Registration Authority (Tailte Éireann)2006 (PRA); 2023 (Tailte Éireann merger)Government of IrelandFolio + Land Registry data, web services for solicitors; XML payloadsActive under Tailte Éireannhttps://www.tailte.ie/
Smart Land Records / eRegistration (Australia, NZ, Canada)2010sVarious national / state cadastresNational variations of digital title-registration systems (PEXA AU, LINZ NZ, Teranet CA Ontario)Active, no cross-border harmonisationhttps://www.pexa.com.au/

Notable threads

  • RETS → RESO Web API as a textbook standards migration. RETS shipped in 1999 — XML-over-HTTP with a custom search grammar, before REST and OData were industry conventions. RESO formally deprecated it in June 2018 but the long tail has dragged on for nearly a decade: as of the RESO Transition Leaderboard, Web API feeds cover ~62% of US subscribers (2024), meaning RETS is still serving ~38%. The pattern is the textbook one — newer standard is technically clearly superior (REST, OData v4.01, JSON, OAuth2, polygon search, structured paging) but the installed base of vendor RETS clients, the per-MLS contractual change overhead, and the fact that “it still works” combine to produce a multi-year tail. By 2026 the leaderboard publishes per-MLS conversion percentages monthly to apply social pressure.

  • MISMO’s reach spans loan origination, servicing, and securitisation — and now closing. MISMO 3.4 schemas are used at every stage of the mortgage lifecycle, and ULDD (built on MISMO 3.0) is mandatory for GSE deliveries. The closing leg — TRID Closing Disclosure + ALTA Settlement Statement — was the last piece to integrate, finalised in the 2015 TRID rule and now routinely round-tripped through MISMO envelopes between lenders and title agents via products like Closing Insight. This is why MISMO appears in both the financial-regulatory family (as the securitisation schema) and here (as the closing-data schema): one standard, two consumer industries.

  • NAR antitrust settlement (March 2024) and the MLS-data ripple. NAR settled the Sitzer/Burnett class action on 15 March 2024 for ~$418M over four years, with practice changes effective 17 August 2024. The MLS-data effects are concrete and observable in schemas: MLS systems can no longer carry broker-compensation fields in their feeds, listings cannot be filtered or sorted by compensation, and MLSs are prohibited from operating any platform offering buyer-broker compensation. RESO’s IDX/VOW/BBO Payloads standards were re-scoped post-settlement to formalise which fields are now off-limits, and buyer-broker negotiation has moved to off-MLS workflows (separate written buyer-agency agreements, signed before any home tour). This is the most consequential schema change in the MLS world in a decade.

  • OSCRE’s open-access pivot and the “smart data highway.” OSCRE spent 20 years as a closed industry consortium publishing CRE data standards behind member-only access. In early 2025 it opened the IDM to the public at no cost, and in February 2026 announced a “smart data highway” vision: rather than just defining terms (“Pump ID”), the IDM will encode relationships (“Pump ID is a synonym for Asset Tag in equipment management context”). This is OSCRE’s attempt to keep pace with LLM-era integrations where downstream tools can disambiguate context if the upstream model exposes it.

  • The regional-MLS fragmentation problem. There are ~600 active MLSs in the US, each with its own membership rules, data-licence terms, and (legacy) RETS endpoint. RESO Data Dictionary has done genuine convergence work — local-field counts are dropping over time — but every MLS still publishes some number of jurisdiction-specific extensions. Aggregators Trestle and MLS Grid exist precisely because no single broker, portal, or vendor can negotiate ~600 individual data agreements; they normalise the feeds into one OData surface. The aggregators themselves are now the de facto integration point for most national platforms.

  • ALTA Best Practices and the post-2020 cybersecurity tilt. ALTA Best Practices started life (2013) as an operational-controls framework — escrow trust accounting, licensing, recording timeliness. The v4.0 rewrite (2023) and v4.2 update (August 2025) shifted the centre of gravity to information security: wire-fraud / business-email-compromise (BEC) defences, identity verification for remote-online-notarisation, signing-agent vetting, and incident response. This tracks the empirical loss data — wire-fraud and BEC are now the dominant loss vectors in residential title insurance — and quietly turns ALTA Best Practices into the de facto cybersecurity baseline for the entire US title industry.

  • UK HM Land Registry’s 2030 digitisation push and the SOAP→REST cliff. HM Land Registry committed in its 2017 Business Strategy and reaffirmed in subsequent transformation plans to comprehensive digital registration of all land in England and Wales by 2030. The data-side workstream is a SOAP→REST API migration (the old e-DRS service is being replaced by a “lightweight” REST suite under the Business Gateway), with an API catalogue currently exposing 15 services covering title, charges, INSPIRE polygons, and price-paid data. The 2030 target also implies automation of “straightforward transactions” like remortgages and registered-property sales — a level of end-to-end digital transaction that no US jurisdiction currently approaches.

Citations

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