This document describes the reconciliation service API, a protocol edited by the W3C Entity Reconciliation Community Group. It is intended as a comprehensive and definitive specification of this API in its given state. Various aspects of this API need to be improved, as hinted by notes throughout this document.

Members of the Community Group are encouraged to contribute to this document by documenting the current behaviour of the reconciliation API. The ReSpec Editor's Guide can be used to learn more about the markup to use in this document.

Introduction

Data Matching on the Web

Integrating data from sources which do not share common unique identifiers often requires matching (or reconciling, merging) records which refer to the same entities. The promises of the Linked Open Data movement, the ability to mix up data from different publishers expressed in a common language (such as RDF) rely on being able to identify identities across services. Due to the Web's decentralized nature, there is nothing preventing a service from publishing a new URI for a resource or concept which is already expressed by another URI.

Various mechanisms exist to state the equivalence between two URIs: for instance, such a correspondence can be stated with the owl:sameAs property [[owl-features]], or using looser notions equivalences defined in SKOS [[skos-primer]]. But such statements must in turn be themselves findable. One can aggregate owl:sameAs statements from various sources to infer identities by transitivity, but this is a subtle art as some data sources can erroneously equate different concepts [[beek-2018]]. After all, any quest towards building a universal identifier system which avoids duplicates is necessarily doomed. Data publishers use different granularities to model the world. Concepts have fluctuating boundaries across languages, cultures and time.

In practice, we can determine if two database records refer to the same entity by comparing their attributes. For instance, two entries about cities bearing the same name, in the same country and with the same mayor are likely to refer to the same city. The reconciliation API that we present here makes it easier to discover such matches. It is a protocol that a data provider can implement, enabling its consumers to efficiently match their own data to the entities represented by the provider.

By nature, reconciliation is a heuristic process. Different entities can have many identical characteristics, leading to false positives. The same entity can be represented in different ways by two databases, for instance by spelling names differently, leading to false negatives. This problem has been extensively studied and many heuristics have been proposed to tackle it [[christen-2012]]. The reconciliation API is agnostic about the particulars of the heuristics involved: it lets data providers choose how they want to determine which of their entities are good candidates for a particular query. What it provides is a web API to let users obtain these candidate entities without having to implement the underlying reconciliation heuristics themselves, nor download the entire contents of the target database.

History of the Reconciliation API

This API was originally designed by Metaweb as a protocol used between Freebase and Gridworks (now known as OpenRefine). Freebase was a free crowdsourced knowledge graph, storing data about a broad range of topics and exposed on the web as linked data. OpenRefine is tool which was originally designed to help populate this knowledge graph by importing data into it. It supports a range of operations which help the user reshape their data to prepare it for ingestion in a data model such as Freebase's. One of these operations is reconciliation, which matches mentions of entities in the local dataset to records in the target database. The reconciliation API was initially introduced to specify how OpenRefine and Freebase could communicate during that process.

The reconciliation API was then turned into a generic protocol that any database could implement. This made it possible to register such a database into OpenRefine by adding it as a Standard Service. This API was implemented by various services, either directly by the service provider itself (for instance the Crossref funder database, Nomisma or the Getty thesaurus) or by a third party as a wrapper sitting on top of other existing web APIs for the service (such as Wikidata or VIAF). Software was also developed to expose a reconciliation endpoint out of any tabular file (reconcile-csv) or by wrapping a SPARQL endpoint (in the OpenRefine RDF extension).

This API was documented on OpenRefine's wiki as a living document which evolved gradually, as OpenRefine improved. In addition to its core feature, fetching reconciliation candidates matching a given query, services are optionally able to implement additional endpoints which ease the integration of the service in OpenRefine's UI, by providing previews for entities (with a Preview Service) and auto-completion for various inputs (with Suggest Services). In 2018, a Data Extension Service was added, letting consumers pull data from the target database once they have reconciled their records.

In 2019 the W3C Entity Reconciliation Community Group was formed, with the intention of promoting and improving this API outside the strict scope of the OpenRefine project. This document is an attempt to better specify this API.

External Resources

A list of known public endpoints is maintained by the community, where they can also be tried out interactively. OpenRefine's wiki also hosts a list of reconciliable data source which also includes non-hosted or discontinued services. Existing clients to the API, such as OpenRefine or Cocoda can be used to interact with reconciliation services.

Versions

This section summarizes the differences between successive versions of the API.

0.1

Initial documentation of the reconciliation API as supported by OpenRefine 3.0 to 3.2.

0.2

Initial improvements to the specifications made by our Community Group. Most of them are backwards-compatible, except for the requirement to support CORS for cross-origin access.

  • Let manifests announce which versions of the protocol are supported by the service
  • Make CORS support mandatory and JSONP support optional
  • Add support for exposing type hierarchies
  • Improve definition of schema space
  • Establish the connection between properties in reconciliation queries and in data extension queries
  • Make 'query' field of reconciliation queries optional
  • Add support for returning matching features in reconciliation candidates
  • Add support for authentication
  • Add support for referencing other reconciliation services in reconciled values returned by data extension
  • Add support for specifying the size of expected reconciliation batch sizes

This Draft

Collection of changes which make the API conform to the REST principles and follow the W3C's guidelines around accessibility, localization and security.

Core Concepts

This section documents the data model behind the reconciliation API. A reconciliation service lets users match their data against entities exposed by the service. Matching can be refined by filtering by type or properties with property values. The purpose of this section is to define these notions.

Entities

An entity is a record in the data source exposed by the service. It comprises the following fields:

id
an identifier, which is a non-empty string. This identifier must be unique among all entities;
name
a name, which is also a non-empty string;
description
an optional description as a human-readable string;
type
an array of types, possibly empty;
Moreover, for each property the entity contains a set of associated property values, possibly empty.

Reconciliation services MUST define in their service manifest a URI template for entities, as defined by [[RFC6570]]. This URI template builds a view URI for each entity, and has id as only variable. For each entity, expanding the template with id being set to the entity's identifier MUST result in a valid URI.

For example, a service which uses Wikidata identifiers for its entities could use http://www.wikidata.org/entity/{id} as URI template for entities. For an entity with identifier Q5, this would expand to http://www.wikidata.org/entity/Q5. Services for which the entity's identifier is already a full URI can use the {+id} template, which disables the escaping of some characters when inserting the identifier in the template. See [[RFC6570]] for more examples of URI templates.

Similarly, it is possible to associate to each matching feature a URL where documentation about the feature is provided, by means of a URI template. Inserting any feature identifier in this template generates the URL for the feature.

Types

A type represents a category of entities. It comprises the following fields:

id
an identifier, which is a non-empty string. This identifier must be unique among all types;
name
a human-readable name, which is a non-empty string;
broader
an optional array of types, each representing a direct (i.e., immediate) broader [[skos-reference]] category of entities.

Properties

A property represents a type of attribute that entities can have in the data source. It comprises the following fields:

id
an identifier, which is a non-empty string. This identifier must be unique among all properties;
name
a human-readable name, which is a non-empty string.

Property Values

A property value can be any of the following:

Service Definition

This section documents how reconciliation services are exposed as HTTP(S) services and how they can announce the features of the API they implement.

The endpoint of a reconciliation service is a URL from which the reconciliation service is offered.

Service Manifest

When the reconciliation service endpoint is queried with a HTTP GET query without parameters, the service manifest MUST be returned.

A service manifest consists of the following fields:

versions
The array of API versions supported by the endpoint, such as ["0.1", "0.2"]. Since this field did not exist in version 0.1, services which do not declare a versions field are expected to only support version 0.1.
name
A human-readable name for the service, generally the name of the database it exposes. In the case where multiple reconciliation services exist for the same database, it is in the interest of a service to bear a meaningful name which will help disambiguating it from others;
defaultTypes
An array of types which are considered sensible default choices as types supplied in reconciliation queries. For services which do not rely on types, this MAY contain a single type with a generic name making it clear that all entities in the database are instances of this type.
documentation
An optional URL with human-readable documentation about the service, for instance giving more information about the data it exposes;
logo
An optional URL of a square image which can be used as the service's logo;
serviceVersion
An optional string which describes the version of the software exposing this service. This is not to be confused with versions which is about the versions of the reconciliation API supported by the service;
view
An object which contains a single field url. Its value is a URI template for entities;
featureView
An optional object which contains a single field url. Its value is a URI template for matching features;
preview
A preview metadata object, supplied if the service offers a preview service;
suggest
An optional object which may contain the following fields, depending on which suggest services are offered:
entity
A boolean indicating if the service supports auto-suggestion of entities;
property
A boolean indicating if the service supports auto-suggestion of properties;
type
A boolean indicating if the service supports auto-suggestion of types;
extend
A data extension metadata, supplied if the service offers a data extension service.
batchSize
The maximum number of reconciliation queries in a single reconciliation query batch. The service MAY respond to batches larger than this number with a 413 HTTP error status code [[RFC7231]]
authentication
An security scheme, supplied if the service supports authentication.
lang
An optional value for the default text-processing language used by this service.
dir
An optional value for the default text direction used by this service.
standardizedScore
An optional boolean indicating if the service returns values between 0 and 100 (inclusive) in the score field of reconciliation candidates. This enables clients to process and display candidates accordingly, e.g. with score percentages or visualizations.

For instance, a service could expose the following minimal service manifest:


      

A more complete example, with some optional services implemented:


      

Overview of Possible Routes

We give here an overview of the routes that reconciliation services MUST and MAY implement. They are all relative to the root endpoint, which we assume here to be /.

/
The root endpoint, which supports the GET method and returns the service manifest. Services MUST support this route;
/reconcile
The route used to submit reconciliation query batches, with the POST method. Services MUST support this route;
/suggest/entity
The route used for auto-completion of entities, with the GET method. Services MAY support this route, as indicated in their manifest;
/suggest/property
The route used for auto-completion of properties, with the GET method. Services MAY support this route, as indicated in their manifest;
/suggest/type
The route used for auto-completion of types, with the GET method. Services MAY support this route, as indicated in their manifest;
/preview
The route used to preview an entity, with the GET method. Services MAY support this route, depending on the presence of a preview metadata object in their manifest;
/extend
The route used to submit data extension queries, with the POST method. Services MAY support this route, depending on the presence of a data extension metadata object in their manifest;
/extend/propose
The route used to obtain data extension property proposals, with the GET method. Services MAY support this route, following what their data extension metadata object in their manifest indicates.

HTTP(S) Access

In the interest of protecting the data sent as reconciliation queries, all endpoints of reconciliation services SHOULD be available over HTTPS [[RFC7230]] [[SECURING-WEB]]. This does not apply to locally hosted services.

Cross-Origin Access

All HTTP(S) endpoints exposed by the service MUST enable access by CORS [[cors]] to enable web-based clients to access the service from a different domain without exposing themselves to untrusted third-party code.

Some clients might only require cross-origin access on some particular endpoints, which are called directly by a web UI. Since this depends on the architecture of the client, this cannot be relied upon and cross-origin access MUST be implemented for all endpoints in a uniform way.

Error Handling and Rate-limiting

Services SHOULD use the broad spectrum of HTTP status codes [[RFC2616]] [[RFC6585]] to expose errors, for instance due to malformed or too frequent queries.

The response body of such error responses is not specified so far.

Authentication

Services MAY request users to provide an authentication token when making queries. They can do so by adding a security scheme to their manifest. Security schemes are defined in [[OPENAPIS]] and support authentication by API key, HTTP Authentication [[RFC7617]], OAuth 2 [[RFC6749]] and OpenID Connect.

For instance, the following security scheme indicates that basic HTTP authentication is required on this endpoint:


        

Requiring an API key passed as a query parameter can be expressed as follows:


        

If a security scheme is provided in the service manifest, all queries to the service MUST provide the corresponding credentials, except for retrieving the service manifest itself. When invalid authentication is supplied in any HTTP request, the service MUST return an HTTP 401 error.

Reconciliation Queries

This section specifies how clients can send reconciliation queries to services and how services respond to them.

Structure of a Reconciliation Query

A reconciliation query consists of the following fields.

conditions
An array of conditions (at least one).
type
An optional type identifier. Supplying such a type allows users to restrict the search to entities which bear this type. Whether this restriction should be a hard constraint or simply induce a change on the reconciliation scores can be determined by the service. In particular, services MAY return candidates which do not belong to the supplied type;
limit
An optional limit on the number of candidates to return, which must be a positive integer;

A condition specifies a constraint that should be matched by the entities to return. It is used to filter the set of candidates (similar to a WHERE clause in SQL), by allowing clients to specify an attribute of entities that should match. It consists of:

matchType
Either name or property, depending on whether the condition relates to entity names or their properties.
pid
A property identifier, to be provided if and only if the matchType is property.
v
one or more property values. If matchType is name, then this value is to be matched to entity names, otherwise to the property values via the supplied pid. The specifics of how this similarity is defined are determined by the service.
required
An optional boolean indicating if a match for the property is required for an entity to enter the list of candidates (i.e. acting like a filter or a WHERE clause in SQL) or optional (i.e. only effecting the entity's rank in the list of candidates). If omitted, the service SHOULD assume the requested value to be false;
matchQuantifier
An optional string to indicate which of the values in v to match. MUST be any (equivalent to boolean OR), all (equivalent to boolean AND), or none (equivalent to boolean NOT). If omitted, the service SHOULD assume the requested value to be any;
matchQualifier
An optional string to indicate how to match the values in v. This can be used for general matching relations like "skos:exactMatch", "skos:closeMatch", etc. or for specific features like spatial matching with geo data (e.g. containment search with "schema:containsPlace" etc.) or custom matching on date fields (e.g. services supporting the [[EDTF]] specification could use "EDTF:Level-0" etc. To allow discovery of supported qualifiers by clients, services that support matchQualifier MUST return the supported matchQualifiers for each property in their property suggest responses. If omitted, the matching behavior is up to the service.

A reconciliation service that supports property assignments SHOULD provide a suggest service for discovering these properties.

A reconciliation query batch is an array of reconciliation queries.

Minimal example of a reconciliation query batch with mandatory fields only:


        

Full example of a reconciliation query batch with all optional fields:


        

For a single property it is possible to provide multiple values as an array. The values provided do not need to have the same type. In the following example a string and a reconciled value are provided as values for the same property.


	

A JSON schema to validate the serialization of a query batch is available.

Reconciliation Query Responses

A reconciliation candidate represents an entity as a response to a reconciliation query. It is proposed to the client as a potential matching entity for this query. It contains the following fields:

id
The identifier of the candidate entity;
name
The name of the candidate entity;
description
The entity description MAY optionally be included;
type
The types of the candidate entity;
score
An optional numeral indicating how well this candidate entity matches the query: a higher score indicates a better match. If candidates are scored, the reconciliation service SHOULD sort candidates in decreasing score order. If standardizedScore is set to true in the service manifest, this value MUST be between 0 and 100 (inclusive);
features
An optional array of matching features;
match
A boolean matching decision, which indicates whether the service considers this candidate good enough to be chosen as a correct match.

A matching feature is a numerical or boolean value which can be used to determine how likely it is for the candidate to be the correct entity. It contains the following fields:

id
A string which identifies the feature, such as "name_tfidf" or "pagerank". This id must be unique among all the matching features returned for a given candidate;
name
A human-readable name, which is a non-empty string.
value
The value of the feature for the candidate, which can be any boolean or numerical value.
Multiple matching features are often used in combination to provide the final matching score (available in the score field). By exposing individual features in their responses, services make it possible for clients to compute matching scores which fit their use cases better.

Example of a reconciliation candidate with all possible fields:


        

A reconciliation result is a set of reconciliation candidates. It is serialized in JSON as an object containing in the field candidates an array of such reconciliation candidate objects.

A reconciliation result batch is an array of reconciliation results given in the same order as in the corresponding reconciliation query batch. When serialized in JSON, it is wrapped in an object under the results field.

Full example of a reconciliation result batch:


        

A JSON schema to validate the serialization of a reconciliation result batch is available.

Sending Reconciliation Queries to a Service

The primary role of a reconciliation service is to translate reconciliation query batches to reconciliation result batches over HTTP.

A reconciliation service MUST support HTTP POST requests at the route /reconcile (relative to its endpoint) with application/json bodies containing a reconciliation query batch.

POST /reconcile <reconciliation query batch>

The service returns the corresponding query batch serialized in JSON.

A Note on Candidate Retrieval and Scoring

The way candidates are retrieved from the underlying database and scored against the query is left entirely at the discretion of the service. However services should retrieve and score the candidates of each query in a batch independently of the other queries in the same batch, or in previous ones. It is also expected that reconciliation queries where query matches exactly the name of an entity in the database and with no other constraint should return at least this entity, unless it is hidden by many namesakes. Similarly, supplying an entity identifier as query should return the corresponding entity as a candidate, with a high score.

Deciding on a scoring method is one of the main difficulties in developing a reconciliation service. Depending on the use case, we might not want a score at all: in cases like geo containment (a place should be inside a specific area) or date ranges (a point in time should be inside a specific time range) the score is irrelevant, as candidates are either in or out. Thus the score attribute is optional. Services are encouraged to expose as many matching features as they deem useful, in particular features which require knowledge of global statistics on the database or other attributes. Examples include:

Name matching
Similarity metrics to compare the entity name and the query;
Entity popularity
Metrics which predict how likely an entity is likely to be refered to, regardless of the query supplied;
Comparison of attributes to query properties
Obtained using similarity metrics to compare the supplied properties and measure their discriminative power;
Type matching
To quantify how well any type supplied in the query corresponds to the candidate's types.
By exposing such features, services make it possible for clients to use a wide range of data matching strategies [[christen-2012]]. This also makes the global candidate scores less opaque.

Many open source reconciliation services are available and these might provide some inspiration concerning indexing and scoring methods when developing new services. See External Resources for some examples.

Preview Service

This section specifies how reconciliation services can provide embeddable HTML previews of their entities, which clients can display in their user interface.

Preview Metadata

Reconciliation services MAY offer a preview service by providing the preview metadata as an object stored in the service manifest under the key preview. It consists of the following fields, all mandatory:

width
The width in pixels of the viewport where to render an entity preview;
height
The height in pixels of the same viewport.

For instance, a service may expose the following preview metadata:


      

Preview Queries

A preview service is queried by resolving the URI template /preview?id={id} relative to the reconciliation endpoint, where id is subsituted by the entity identifier. The URL must resolve to an HTML document, which MUST be viewable in an HTML viewport whose dimensions are determined by the preview metadata.

For instance, assuming that the reconciliation API is running at /api and serves the example preview metadata above, the service could respond to a preview request as follows:

       

Suggest Services

This section specifies how reconciliation services can provide auto-complete endpoints for their entities, properties and types. A reconciliation service can offer a suggest service for any of these three classes. For instance, a service which only exposes a single type might not want to expose a suggest service for types. These suggest services can be used by clients to let users select an entity, property or type manually, at various stages of their reconciliation workflows. Suggest services for entities, properties and types are declared independently in the service manifest.

Suggest Endpoints

When supported, the suggest endpoints are located at the following URIs, relative to the service's root endpoint:

/suggest/entity
/suggest/property
/suggest/type

Suggest Queries

A suggest service MUST accept GET queries with the following URL-encoded parameters:

prefix
The string input by the user in the auto-suggest-enabled field; depending on the data users are working with, they might want to select a suggestion from all available types, properties, or even entities; to allow that, services MAY send all suggestions if the prefix is empty, and clients SHOULD provide a way to send the empty prefix;
cursor
An optional integer to specify the number of suggestions to skip: this can be used by clients to fetch more suggestions.

Suggest Responses

A response to a suggest query consists of the following fields:

result
An array of items, which can be entities, properties or types depending on which of these the service is provided for. Each such object can contain the following fields:
id
The identifier of the entity, property or type suggested;
name
Its corresponding human-readable name, to be displayed prominently to the user;
description
An optional description which can be provided to disambiguate namesakes, providing more context. This could for instance be displayed underneath the name;
notable
When suggesting entities only, this field can be used to supply some important types (not necessarily all types) of the suggested entity. The value must be an array of either type identifiers (as strings) or type objects, containing an id and name field which represent the type.
matchQualifiers
When suggesting properties only, an optional array of objects, each containing an id and name field, which represent the property's matchQualifiers supported in reconciliation queries.

The key notable comes from a notion of notable types that existed in Freebase.

For instance, a suggest service for entities could return the following response:


        

A suggest service for properties could return the following response:


        

And a suggest service for types could return the following response:


        

JSON schemas to validate suggest responses are available for entities, for properties and for types.

General Expectations about Suggest Services

It is generally expected by users that an entity suggest query where prefix is the name of an entity should return this entity in the suggest response, unless that entity is hidden behind many other namesakes. Similarly, supplying an entity identifier as prefix should return this entity in the suggest response. Analogous expectations apply for property and type suggest services.

As the prefix name suggests, suggest services are expected to perform prefix search on their database of records, such that a suggest service can be used to provide auto-completion as users type names or identifiers in a field.

Data Extension Service

This section specifies how reconciliation services can let clients fetch the values of some properties on a selection of entities.

A data extension service MUST support data extension query requests.

A data extension service SHOULD provide data extension property proposals.

A data extension service MAY support data extension property settings.

Data Extension Metadata

The data extension metadata is an object stored in the service manifest in the extend field. It consists of the following settings, all optional:

proposeProperties
A boolean indicating if the service supports data extension property proposal;
propertySettings
An array of data extension property settings.

A data extension property setting consists of:

id
A unique identifier for the setting;
name
A human-readable name, which is used when presenting the setting to the user in a form;
type
A data type, which can be one of the strings "number", "text", "checkbox", or "select". This determines which type of value the property setting is expected to store: clients SHOULD render this setting with the corresponding HTML element;
default
A default value for the setting, when not provided or left untouched by the user;
helpText
A help text, which describes the meaning of the field to the user. This is meant to be a short string that can be displayed alongside the corresponding form field;
choices
If type is select, an array of property setting choices.

Example of data extension metadata with all optional fields:


        

Data Extension Property Proposals

A data extension property proposal service returns properties for a given type identifier.

If the reconciliation service supports data extension property proposals, it MUST support HTTP GET requests to the endpoint /extend/propose (relative to the reconciliation endpoint) with a type query parameter containing a type identifier.

The service SHOULD support an optional limit query parameter to control the number of proposed properties.

GET /extend/propose?type=<type identifier>[&limit=<limit>]

A data extension property proposal response consists of:

properties
An array of proposed properties. These properties are suggested as fields that could be potentially fetched via data extension for entities of the type provided in the query;
type
The type identifier supplied in the query;
limit
Optionally, an integer to indicate the requested limit;

Example of a data extension property proposal response:


        

Data Extension Query Requests

A data extension query request lets clients fetch the values of some properties on a selection of entities.

The fact that a reconciliation service offers data extension MUST be announced by including a data extension metadata in the extend field of the service manifest.

A data extension service MUST support HTTP POST requests at /extend (relative to the reconciliation endpoint) with application/json bodies containing a data extension query.

POST /extend <data extension query>

A data extension query consists of:

Example of a data extension query:


        

Data Extension Responses

A data extension response consists of metadata and rows.

The metadata contains the properties used for data extension, as requested in the data extension query. If properties have entities as values, they MAY specify a type in the metadata.

The rows object contains, for each entity identifier in the data extension query, for each property identifier in the metadata, the property values of that property in that entity. If the property values are entities, their identifiers are expected to be valid entities for the service at hand. If that is not the case, the service MUST specify in the meta section the endpoint of another reconciliation service for which the entity identifiers are valid, i.e., inserting them into the entity view template of that other service yields valid URIs. This endpoint is specified on a column-per-column basis.

Response example for the data extension query from the previous example:


        

Internationalization Considerations

The following sections rely on terminology from the W3C internationalization best practices for spec developers, in particular on the distinction of two types of language declaration:

The language of the intended audience, also referred to as language metadata, is used to describe the language(s) of the intended audience of resources as a whole. In the context of reconciliation, this is relevant e.g. for setting the user interface language in a reconciliation client, providing user-facing text in the user's preferred language.

The text-processing language on the other hand declares the single language in which a specific range of text is actually written in, to support features like text-to-speech, spell checking, or hyphenation. In the context of reconciliation, this distinction is importat since the actual data being reconciled will often be in a different language than the client's user interface.

Language of the intended audience

Following [[RFC9110]], services SHOULD support the Accept-Language header to let clients specify the language of the intended audience in which user-facing text is returned. If clients set the Accept-Language header, the requested language(s) MUST be provided as well-formed [[BCP 47]] language tags. Services MAY use the Content-Language header in their responses to expose the language(s) of the intended audience(s) of each response. If services set the Content-Language header, they MUST use valid (i.e. found in the [[IANA Language Subtag Registry]]) [[BCP 47]] tags.

Examples of user-facing text in service responses are: the name of the service and the name of property configuration fields in the manifest, the name and description of entities, types and properties, the contents of the entity preview pages, and the documentation linked in the manifest.

Text-processing language

All objects used in this protocol (entities, types, properties, queries, candidates, features, etc.) MAY declare an explicit text-processing language in a lang field. The lang value MUST be a single valid (i.e. found in the [[IANA Language Subtag Registry]]) [[BCP 47]] language tag. This text-processing language applies to the natural language fields of the object: name, description, query (for reconciliation queries), v and str (for property values). Nested objects inherit the text-processing language of their parent, and can override it by setting their own lang value (see example below). A default text-processing language for any natural language string returned or processed by a service MAY be set in the lang field of the service manifest. Client and service implementors SHOULD consider the text-processing language to ensure correct processing of natural language content.

In the following example, we first set the text-processing language for a reconciliation query to en, which is inherited by the first property, and overridden in the second property with zh-Hant:


        

Text direction

All objects returned by reconciliation services (entities, types, properties, candidates, features, etc.) MAY declare an explicit text base direction in a dir field. The dir value MUST be ltr for left-to-right, rtl for right-to-left, or auto for determining the direction by examining the content of each JSON field. This base direction applies to the natural language fields of the object: name and description (for candidates etc.), v and str (for property values). Nested objects inherit the base direction of their parent, and can override it by setting their own dir value. A default base direction for any natural language string returned or processed by a service MAY be set in the dir field of the service manifest. If no explicit base direction is given, left-to-right is considered the default base direction. Clients SHOULD consider the base direction to ensure correct rendering of content, e.g. by setting corresponding dir attributes when rendering JSON responses in HTML. For instance, rendering a Persian label for 'Yahoo!' like یاهو! right-to-left will correctly display as یاهو!.

In the following example, we first set the base direction for a data extension response row to ltr, which is inherited by the first property, and overridden in the second property with rtl:


        

Accessibility Considerations

Reconciliation clients provide user interfaces for creating reconciliation queries and reviewing reconciliation candidates, including preview and suggest services, as well as for interacting with data extension services, including property proposals and configuration of property settings. These user interfaces SHOULD be implemented ensuring [[accessibility]] for all people, whatever their hardware, software, language, location, or ability.

Visual rendering

The preview service provides HTML content to reconciliation clients. Using HTML allows services to provide non-text alternatives for text content, as well as semantically rich content (structure, styled text, hyperlinks, etc). Reconciliation services SHOULD ensure [[accessibility]] of this HTML content (avoid fixed font sizes, provide alternative text for images etc). The service's preview metadata contains the suggested width and height to display the preview content. Reconciliation clients SHOULD consider adjusting these values as required for supporting accessibility features like UI scaling.

Except for the preview content and size, all data involved in the reconciliation and data extension process is text-based and contains no specifics about visual rendering. Reconciliation clients SHOULD ensure [[accessibility]] for this text content (font resizing, screen reader support etc.) based on the technology of the underlying platform, which will typically implement the details of visual text rendering and user interface customization.

Content semantics

The main content presented to users is provided in reconciliation results and data extension responses. Both support name fields for all identifiable objects, in particular entities, types, properties, and matching features. These SHOULD be used by reconciliation clients to provide useful labels for displaying and linking identifiable entities. The structural semantics of the content provided by reconciliation services allows different presentations (as pages, tables, etc.) in reconciliation clients. Being fully text- and JSON-based, content can be modified by third-party tools to enhance accessibility.

Security Considerations

Preventing Abuse

Other considerations

Privacy Considerations

Network data

Persistent data

JSON Schemas

This appendix provides JSON schemas [[json-schema]] which can be used to validate the JSON serialization of various elements as specified by these specifications.

Manifest Schema

The manifest schema can be used to validate a service manifest.

      

Reconciliation Query Batch Schema

The reconciliation query batch schema can be used to validate the JSON serialization of any reconciliation query batch, i.e. the payload of a GET/POST to the reconciliation endpoint.

      

Reconciliation Result Batch Schema

The reconciliation result batch schema can be used to validate the JSON serialization of any reconciliation result batch.

      

Suggest Entities Response Schema

The suggest entities response schema can be used to validate the JSON serialization of any suggest response for entities.

      

Suggest Properties Response Schema

The suggest properties response schema can be used to validate the JSON serialization of any suggest response for properties.

      

Suggest Types Response Schema

The suggest types response schema can be used to validate the JSON serialization of any suggest response for types.

      

Data Extension Property Proposal Schema

The data extension query schema validates data extension property proposal responses.

      

Data Extension Query Schema

The data extension query schema validates data extension queries.

      

Data Extension Response Schema

The data extension response schema validates data extension responses.