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# 1. Introduction
This document provides server implementation best practices for SpatioTemporal Asset Catalog (STAC) search and catalog services that allow for standardized and harmonized access to metadata and data for CEOS agencies, including CWIC and FedEO.

STAC is a lightweight, JSON-based language that is asset-oriented, self-navigable and tailored towards the spatial and temporal domain. 

It also provides a framework for achieving federated discovery in much the same way as OpenSearch. Where STAC has an advantage over OpenSearch is its widespread adoption in the earth science informatics community. 
## 1.1 Purpose of document

The STAC ecosystem comprises both API-related and metadata-related specifications.
This document provides server implementation Best Practices for STAC-based metadata publication and related discovery services allowing for standardized and harmonized access to metadata and data for CEOS agencies.

The purpose of this document is to achieve the following,
- Promote the use of the STAC standard as a means of data discovery for Earth Data providers
- Define the expectations and requirements of candidate STAC implementations
- Remove ambiguity in implementation where possible
- Facilitate the aggregation of results between disparate Earth Data providers via STAC common standards
- Allow for clients to access search engines via STAC capabilities with no a priori knowledge of specific implementations
- Facilitate smooth integration between related STAC implementations, such as a dataset resource collection that refers to granule resource collections from another provider
- Replace the existing [CEOSS WGISS Integrated Catalog](https://ceos.org/ourwork/workinggroups/wgiss/access/cwic/) (CWIC) and [WGISS Connected Data Assets](https://ceos.org/ourwork/workinggroups/wgiss/access/connected-data-assets/) (CDA) infrastructure, based on the [OpenSearch API](https://github.com/dewitt/opensearch), with the STAC API and STAC catalogs
## 1.2 Document overview

The document is organized as follows:

- Chapter 1 is the introduction of the document.
- [Chapter 2: Objectives and needs](objectives-needs.md) gives an overview of objectives and needs.
- [Chapter 3: Best Practices](best-practices.md) introduces the categories of Best Practices and presents best practices for catalogs and metadata appicable to collections and granules.

The following chapters present Best Practices for one particular topic:

- [Chapter 4: Granule Catalog Best Practices](granule-catalogs.md)
- [Chapter 5: Collection Catalog Best Practices](collection-catalogs.md)
- [Chapter 6: Granule Metadata Best Practices](granule-metadata.md)
- [Chapter 7: Collection Metadata Best Practices](collection-metadata.md)
- [Chapter 8. Federation Best Practices](federation.md)

## 1.3 Terms, definitions and abbreviated terms

### 1.3.1 Terms and Definitions 

|  |   |  
| -------- | --------- | 
| `Analysis Ready Data` | Satellite data that have been processed to a minimum set of requirements and organized into a form that allows immediate analysis with a minimum of additional user effort and interoperability both through time and with other datasets. |
| `Granule` | A granule is the finest granularity of data that can be independently managed. A granule usually matches the individual file of EO satellite data.  | 
| `Collection` | A collection is an aggregation of granules sharing the same product specification. A collection typically corresponds to the series of products derived from data acquired by a sensor on board a satellite and having the same mode of operation. [[RD01]](#RD01) | 
| `Interface` | Named set of operations that characterize the behavior of an entity.  | 
| `Metadata` | Information about a resource [[RD02]](#RD02).  | 
| `Metadata element` | Discrete unit of metadata [[RD02]](#RD02).  | 


### 1.3.2 Acronyms

|  |   |  
| -------- | --------- | 
| `API` | Application Programming Interface |
| `ARD` | Analysis Ready Data |
| `CEOS` | Committee on Earth Observation Satellites   |  
| `CQL` | Common Query Language   |  
| `DIF-10` | Directory Interchange Format Version 10   |  
| `EO` | Earth Observation   |  
| `GCMD` | Global Change Master Directory   |  
| `HATEOAS` | Hypertext As The Engine Of Application State  |
| `IDN` |  International Directory Network  | 
| `JSON` | JavaScript Object Notation  | 
| `OGC` | Open Geospatial Consortium  | 
| `OSDD` | OpenSearch Description Document  |
| `S3` | Simple Storage Service  |
| `STAC` | Spatiotemporal Asset Catalog  |
| `WGISS` | Working Group on Information Systems and Services  | 

## 1.4 References

### 1.4.1 Applicable documents


| **ID**  | **Title** | 
| -------- | --------- | 
| `AD01` <a name="AD01"></a> | [STAC Catalog Specification, v1.0.0](https://github.com/radiantearth/stac-spec/blob/v1.0.0/catalog-spec/catalog-spec.md) | 
| `AD02` <a name="AD02"></a> | [STAC Collection Specification, v1.0.0](https://github.com/radiantearth/stac-spec/tree/v1.0.0/collection-spec) | 
| `AD03` <a name="AD03"></a> | [STAC Item Specification, v1.0.0](https://github.com/radiantearth/stac-spec/tree/v1.0.0/item-spec)   | 
| `AD04` <a name="AD04"></a> | [STAC API Specification, v1.0.0](https://github.com/radiantearth/stac-api-spec/tree/release/v1.0.0)  | 
| `AD05` <a name="AD05"></a> | [STAC API - Item Search, v1.0.0](https://github.com/radiantearth/stac-api-spec/tree/release/v1.0.0/item-search) |
| `AD06` <a name="AD06"></a> | [STAC API - Filter Extension](https://github.com/stac-api-extensions/filter) |
| `AD07` <a name="AD07"></a>| [STAC API - Collection Search](https://github.com/stac-api-extensions/collection-search) |
| `AD08` <a name="AD08"></a> | [OGC17-069r3, OGC API - Features - Part 1: Core](https://docs.opengeospatial.org/is/17-069r3/17-069r3.html) | 
| `AD09` <a name="AD09"></a> | [OGC17-079r2, OGC API - Features - Part 3: Filtering](https://docs.ogc.org/is/19-079r2/19-079r2.html)  | 
| `AD10` <a name="AD10"></a> | [OGC21-065r2, Common Query Language (CQL2)](https://docs.ogc.org/is/21-065r2/21-065r2.html)  | 
| `AD11` <a name="AD11"></a> | [RFC 7946 - The GeoJSON Format](https://datatracker.ietf.org/doc/html/rfc7946) | 
| `AD12` <a name="AD12"></a>| [JSON Schema: A Media Type for Describing JSON Documents, draft-handrews-json-schema-02](https://datatracker.ietf.org/doc/html/draft-handrews-json-schema-02) |
| `AD13` <a name="AD13"></a>| [STAC Scientific Citation Extension Specification, v1.0.0](https://github.com/stac-extensions/scientific) |
| `AD14` <a name="AD14"></a>| [STAC Electro-Optical Extension Specification, v1.1.0](https://github.com/stac-extensions/eo) |
| `AD15` <a name="AD15"></a>| [STAC SAR Extension Specification, v1.3.0](https://github.com/stac-extensions/sar) |
| `AD16` <a name="AD16"></a>| [STAC Satellite Extension Specification, v1.0.0](https://github.com/stac-extensions/sat) |
| `AD17` <a name="AD17"></a>| [STAC Versioning Indicators Extension Specification, v1.2.0](https://github.com/stac-extensions/version) |
| `AD18` <a name="AD18"></a>| [STAC View Geometry Extension Specification, v1.0.0](https://github.com/stac-extensions/view) |
| `AD19` <a name="AD19"></a>| [STAC Projection Extension Specification, v1.0.0](https://github.com/stac-extensions/projectionw) |
| `AD20` <a name="AD20"></a>| [STAC Timestamps Extension Specification, v1.0.0](https://github.com/stac-extensions/timestamps) |
| `AD21` <a name="AD21"></a>| [STAC Processing Extension Specification, v1.2.0](https://github.com/stac-extensions/processing) |
| `AD22` <a name="AD22"></a>| [STAC Hyperspectral Imagery Extension Specification, draft](https://github.com/stac-extensions/hsi) |
| `AD23` <a name="AD23"></a>| [STAC Landsat Extension Specification, v1.1.1](https://landsat.usgs.gov/stac/landsat-extension/v1.1.1/schema.json) |
| `AD24` <a name="AD24"></a>| [STAC Alternate Assets Extension Specification, v1.2.0](https://github.com/stac-extensions/alternate-assets) |
| `AD25` <a name="AD25"></a>| [STAC Item Assets Definition Extension Specification, v1.0.0](https://github.com/stac-extensions/item-assets) |
| `AD26` <a name="AD26"></a>| [STAC Web Map Links Extension Specification, v1.3.0](https://github.com/stac-extensions/web-map-links) |
| `AD27` <a name="AD27"></a> |[STAC API - Free Text Search](https://github.com/stac-api-extensions/freetext-search)|
| `AD28` <a name="AD28"></a>| [STAC CEOS-ARD Extension Specification](https://github.com/stac-extensions/ceos-ard) |
| `AD29` <a name="AD29"></a>| [STAC Themes Extension Specification, v1.0.0](https://github.com/stac-extensions/themes) |
| `AD30` <a name="AD30"></a>| [CEOS-ARD Product Family Specifications](https://ceos.org/ard) |
| `AD31` <a name="AD31"></a>| [STAC Product Extension Specification, v1.0.0](https://github.com/stac-extensions/product) |
| `AD32` <a name="AD32"></a>| [STAC Authentication Extension Specification, v1.1.0](https://github.com/stac-extensions/authentication) |
| `AD33` <a name="AD33"></a>| [STAC Grid Extension Specification, v1.1.0](https://github.com/stac-extensions/grid) |
| `AD34` <a name="AD34"></a>| [STAC File Extension Specification, v2.1.0](https://github.com/stac-extensions/file) |


### 1.4.2 Reference documents

| **ID**  | **Title** | 
| -------- | --------- | 
| `RD01` <a name="RD01"></a> | [CEOS OpenSearch Best Practice Document, Version 1.0, CEOS-OPENSEARCH-BP-V1.3](https://ceos.org/document_management/Working_Groups/WGISS/Documents/WGISS%20Best%20Practices/CEOS%20OpenSearch%20Best%20Practice.pdf)  |
| `RD02` <a name="RD02"></a> | [ISO 19115-1:2014, Geographic Information – Metadata – Part 1: Fundamentals, First Edition 2014-04-01](https://www.iso.org/standard/53798.html)  |
| `RD03` <a name="RD03"></a> | [OGC23-038, Best Practice for Common Band Names of Optical and Radar Sensors](https://portal.ogc.org/files/?artifact_id=104980&version=1) - Not yet available.  |
| `RD04` <a name="RD04"></a> | [OGC13-026r9, OpenSearch Extension for Earth Observation](https://docs.ogc.org/is/13-026r9/13-026r9.html) |
| `RD05` <a name="RD05"></a> | [WGISS Data Collections Management Practices White Paper](https://ceos.org/ourwork/workinggroups/wgiss/documents/) - Not yet available. |
| `RD06` <a name="RD06"></a> | [CEOS WGISS Persistent Identifiers Best Practice, Version 1.4, CEOS/WGISS/DSIG/PIDBP](https://ceos.org/document_management/Working_Groups/WGISS/Documents/WGISS%20Best%20Practices/CEOS%20Persistent%20Identifier%20Best%20Practice.pdf) |
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