OpenSearch Specification Overview

The OpenSearch specification is an open-source, community-driven project that aims to provide a standardized way of searching and analyzing data. It's built on top of the Apache Lucene library.

OpenSearch is designed to be highly scalable and flexible, making it suitable for a wide range of use cases, from small-scale applications to large-scale enterprise deployments. This is achieved through its modular architecture, which allows developers to easily add or remove features as needed.

The specification is maintained by the OpenSearch project, which is led by Amazon Web Services, and is released under the Apache License 2.0. This ensures that the specification remains open and accessible to anyone who wants to contribute or use it.

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The Requirements Class: Core is a fundamental part of the OpenSearch specification, defining the core requirements for a compliant interface. It outlines the necessary dependencies and requirements for a successful implementation.

A core requirement is that the interface must support HTTP 1.1, as well as the feature-collection and diagnostics requirements classes. This ensures that the interface can handle search responses and exceptions correctly.

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The core requirements class also defines two main requirements: feature-collection and exceptions. The feature-collection requirement ensures that search responses comply with the feature-collection requirements class and have an HTTP Status Code of 200.

In the event of fatal exceptions, the exceptions requirement ensures that search responses comply with the exceptions requirements class and have an HTTP Status Code different from 200.

Here's a summary of the core requirements:

These core requirements provide a solid foundation for building a compliant OpenSearch interface, ensuring that it can handle search responses and exceptions correctly.

The Query element is a crucial part of an OpenSearch description document, allowing search clients to supply search requests. It corresponds to the search parameters in a URL template and includes core search parameters explicitly defined as Query attributes.

To provide an example search request, at least one Query element with role="example" should be included in each description document. This allows search clients to test the search engine.

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Custom parameters can be added via namespaces as needed, and a Query element with role="request" should be provided in each search response so that search clients can recreate the current search. The totalResults attribute is optional and specifies the expected number of results to be found if the search request were made.

Here are some key Query element attributes:

With these attributes in mind, you can create a search interface that meets the requirements of the OpenSearch specification.

An OPDS Catalog MAY provide a search facility through an [OpenSearch] description document. Links to [OpenSearch] description documents MUST use the "search" relation value and the "application/opensearchdescription+xml" media type as defined in the "Autodiscovery" section of the [OpenSearch] specification.

The search interface SHOULD use the media type associated to OPDS Catalogs. This means you can provide a search facility that's tailored to your catalog's needs.

An OPDS Catalog MAY also provide more advanced possibilities for its search endpoint, using one or more fully qualified parameters from the Atom namespace such as: atom:authoratom:contributoratom:title

These parameters can help you provide a more robust search experience for your users. For example, you could use atom:author to search for items by a specific author.

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In an [OpenSearch] description document, the search interface SHOULD use the media type associated to OPDS Catalogs. This ensures that your search interface is compatible with OPDS Catalogs.

To provide a search endpoint that supports both basic (keyword based) and advanced search, an OPDS Catalog could provide the following template in its [OpenSearch] Description document: http://example.com/search?q=gardeninghttp://example.com/search?q=gardening&author=smithhttp://example.com/search?author=druckerhttp://example.com/search?author=ferriss&title=four

This template allows you to support a range of search queries, from simple keyword searches to more advanced searches with multiple parameters.

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When you receive a search response, you'll often get a lot of useful information along with the results. This includes the total number of results, which in one example is 4,230,000.

The response also includes information about the current page of results, such as the number of items per page, which is 10 in the example. This means you're currently looking at results 21-30.

You can also use the response to regenerate the request from the beginning of the results by following the instructions in the query tag. For example, you can use the search term "New York History" and start from the beginning of the results by setting the startPage parameter to 1.

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The response will also include links to other pages of results, such as the first page, previous page, next page, and last page. For instance, the first page of results in Atom format can be found at http://example.com/New+York+History?pw=1&format=atom.

You can also use the response to find the URL to get the next page of results, which is http://example.com/New+York+History?pw=4&format=atom in the example. Similarly, the URL to get the last page of results is http://example.com/New+York+History?pw=4229991&format=atom.

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OpenSearch description documents can be extended as long as foreign elements and attributes are associated with an explicit XML namespace. Clients should ignore unrecognized foreign elements and continue processing the document.

To extend an OpenSearch description document, all foreign elements and attributes must have an explicit XML namespace. This allows for flexibility and customization of the document without breaking its functionality.

An OpenSearch description document can include a reference to other OpenSearch description documents by including "link" elements on search results. These elements should have the following attributes: type="application/OpenSearchdescription+xml", rel="search", href=[URI of an OpenSearch description document], and title=[human-readable plain text string describing the search engine].

Here are the attributes for the "link" elements that reference other OpenSearch description documents:

OpenSearch description documents can be extended as long as all foreign elements and attributes are associated with an explicit XML namespace. Clients should ignore unrecognized foreign elements and continue processing the document normally.

You can extend OpenSearch description documents by including "link" elements on search results with specific attributes and values. These "link" elements can reference other OpenSearch description documents.

An OpenSearch description document can include a reference to another document by using the "link" element with the correct attributes and values. This is similar to how RSS-based search results with an OpenSearch autodiscovery link element work.

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In the OpenSearch specification, certain key words have specific meanings that are used throughout the document. These words, such as MUST and SHOULD, are interpreted as described in RFC2119.

The key words in the specification are used to convey the level of requirement or recommendation for certain actions or behaviors.

The specification also defines a set of terminology that is used consistently throughout the document. This terminology is used to ensure clarity and precision in the language used.

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In this section, we'll explore the notational conventions used in this document. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are used to convey specific levels of importance.

These key words are interpreted as described in RFC2119, a widely recognized standard for internet protocols.

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In this specification, terminology is used to define specific concepts and ideas.

The following terminology is used: the specification itself uses terminology to clarify and define its concepts, making it easier to understand and work with.

This terminology is essential for clear communication and collaboration among developers, users, and other stakeholders.

The terminology used in this specification is consistent throughout, ensuring that everyone is on the same page.

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To map vocabulary to XML, you need to refer to the table provided in the OpenSearch specification. This table maps JSON and vocabulary properties to their equivalent properties in the OpenSearch Atom/XML response encoding.

The JSON property name is matched to the JSON-LD property name, which has been compacted according to the normative JSON-LD context provided in annex B.2 of the specification.

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OGC 13-026r9 is a standard for encoding geospatial data, which is often used in conjunction with JSON for data exchange and storage.

The standard defines a set of rules for mapping OGC 13-026r9 elements to JSON properties, ensuring data consistency and interoperability.

A JSON object is used to represent the root element, with properties mapping directly to OGC 13-026r9 elements, such as 'type' and 'properties'.

The 'type' property maps to the 'type' element in OGC 13-026r9, indicating the type of feature being represented, such as 'Point' or 'Polygon'.

The 'properties' property contains a JSON object with key-value pairs that correspond to the feature's attributes, like 'name' and 'description'.

OGC 13-026r9 elements like 'geometry' and 'coordinates' are also mapped to specific JSON properties, ensuring accurate representation of spatial data.

The mapping rules are designed to be flexible and extensible, allowing for easy adaptation to different use cases and data models.

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The Vocabulary to XML Mapping is a crucial step in the mapping and encoding process.

A table is provided to map JSON and Vocabulary Properties to their equivalent properties in the OpenSearch Atom/XML response encoding, as specified in [OR14], [OR14], [OR20].

The table is based on the JSON-LD property names, which are compacted according to the normative JSON-LD context provided in annex B.2 of the current document.

The JSON property name in the table corresponds to the JSON-LD property name, which is used to identify the equivalent property in the OpenSearch Atom/XML response encoding.

The OpenSearch Atom/XML response encoding is a standard for encoding search results in XML, and it's used to provide a common format for search engines to return results in.

By using this table, developers can easily map their JSON and Vocabulary Properties to the equivalent properties in the OpenSearch Atom/XML response encoding, making it easier to integrate their applications with search engines.

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Oasis SearchRetrieve APD Mapping is a crucial aspect of mapping and encoding. The table below compares the abstract elements from the searchRetrieve Abstract Protocol Definition (APD) with the OpenSearch actual elements and the elements proposed in the current specification.

The numberOfItems element from the APD is mapped to the totalResults element in OpenSearch, and to $.totalResults in JSON.

In OpenSearch, the numberOfGroups element is not present, but it is mapped to an empty string in the current specification. Similarly, the resultSetId element is not present in OpenSearch, but it is mapped to an empty string in the current specification.

The item element from the APD is mapped to a defined response schema, such as an entry in ATOM 1.0, in OpenSearch. In JSON, it is mapped to $.features[*] (GeoJSON Feature).

The nextPosition element from the APD has a specific mapping in OpenSearch, but it is not present in the current specification. The diagnostics element is not present in either OpenSearch or the current specification.

The echoedRequest element from the APD is mapped to the value of the href attribute for the link element with the rel attribute set to "self" in OpenSearch. In JSON, it is mapped to $.id$.queries.request.

Here is a summary of the mappings:

The startIndex and itemsPerPage elements are not present in the APD, but they are present in OpenSearch and mapped to $.startIndex and $.itemsPerPage in JSON, respectively. The Query element is not present in the APD, but it is present in OpenSearch and mapped to $.queries in JSON.

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Error handling and exceptions are crucial aspects of the OpenSearch specification. The specification defines two main requirements classes for exceptions: req/exceptions and req/core/exceptions.

The req/exceptions class has a dependency on HTTP 1.1 and requires a status code in the HTTP header and an ExceptionReport object in the HTTP body. This is defined in requirement 20 of the req/exceptions class.

In case of fatal exceptions, search responses should comply with the req/exceptions requirements class and have an HTTP status code different from 200, as stated in requirement 2 of the req/core/exceptions class.

A compliant OpenAPI description for an OpenSearch interface should contain a Response Object that shows how a FeatureCollection is returned when the HTTP status code is 200, while an ExceptionReport object is returned in case of exceptions.

Here's a summary of the requirements for exception handling:

In summary, exception handling is a critical aspect of the OpenSearch specification, and compliance with the req/exceptions and req/core/exceptions requirements classes is essential for a successful implementation.