docs: initial commit for "search"

README.md

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 <!-- More information about creating your scope with links to examples -->
 <!-- https://contribute.cncf.io/maintainers/governance/charter/ -->
 
-- Define a set of query interfaces that can standardized across various software ecosystems.
+- Define a set of [query interfaces](docs/search/search.md) that can standardized across various software ecosystems.
 
 ## Communications
 

docs/search/search.md

@@ -0,0 +1,126 @@
+---
+tags: cncf,wg-artifacts
+breaks: false
+---
+
+# Search API
+
+The [distribution spec](https://github.com/opencontainers/distribution-spec)
+allows for OPTIONAL [extensions](https://github.com/opencontainers/distribution-spec/blob/main/extensions/README.md) that registry operators may
+implement.
+
+```http
+GET /v2/_<extension>/<component>/<module>[?<key>=<value>&...]
+```
+
+One use case that is rising in prominence is standardized _search_ capability
+within registries. This capability can be organized under _cncf as follows.
+
+```http
+GET /v2/_cncf/ext/search[?<key>=<value>&...]
+```
+
+The prefix `/v2/_cncf` is chosen so that it is compatible with OCI and yet can independently be developed.
+
+## Search vs List?
+
+In this document, if not explicitly called out, it is understood that Search is
+a truncated List based on certain criteria.
+
+## Search Use Cases
+
+Search for:
+
+- Repository name
+
+Return a list of repositories matching _name_. If _name_ is not specified, return all repositories (similar to /v2/_catalog query)
+
+```http
+GET /v2/_cncf/ext/search[?repository=<name>]
+```
+
+** For all the following search queries, an additional _repository=\<repository\>_ query param can be added to further qualify the search.
+
+- Image name
+
+Return a list of images in a _repository_ matching _name_. If _name_ is not specified, return all images (similar to /v2/<>/tags/list query)
+
+```http
+GET /v2/_cncf/ext/search[?repository=<repository>&image=<name>]
+```
+
+- MediaType
+
+Return a list of images matching _name_ media-type. If _name_ is not specified, return all images.
+
+```http
+GET /v2/_cncf/ext/search[?mediaType=<name>]
+```
+
+- ArtifactType
+
+Return a list of images matching _name_ artifact-type. If _name_ is not specified, return all images.
+
+```http
+GET /v2/_cncf/ext/search[?artifactType=<name>]
+```
+
+- Annotation
+
+Return a list of images matching _name_ annotation. If _name_ is not specified, return all images.
+
+```http
+GET /v2/_cncf/ext/search[?annotation=<name>]
+```
+
+- Digest
+
+Return a list of images matching _hash_ digest. If _hash_ is not specified, return all images.
+
+```http
+GET /v2/_cncf/ext/search[?digest=<hash>]
+```
+
+- Free-form global search
+
+Return a list of repositories and images matching _name_ name. If _name_ is not specified, return all repositories and images.
+
+```http
+GET /v2/_cncf/ext/search[?global=<key>]
+```
+
+- Artifact content search
+
+Return a list of images containing a _key_ within artifact contents.
+
+```http
+GET /v2/_cncf/ext/search[?artifactType=<application/spdx>&key=<key>]
+```
+
+## Prefix Match
+
+TBD
+
+## Regex
+
+TBD
+
+## Pagination
+
+Refer to [listing tags](https://github.com/opencontainers/distribution-spec/blob/main/spec.md#listing-tags) section.
+
+## Implementation Guidelines
+
+Not to prescribe an implementation but [GraphQL](https://en.wikipedia.org/wiki/GraphQL) could be a choice.
+TBD
+
+## Scalability
+
+When a registry has a very large number of repositories and images, then compiling and returning the results could be problematic.
+TBD
+
+## References
+
+[OCI Distribution Spec Extensions](./_cncf.md)
+
+[CNCF WG Artifacts](https://github.com/cncf-tags/wg-artifacts)