1. EO Data Access Protocol
HMA for Science SRR
EO Data Access Protocol
SRR
16 May 2013, ESRIN Frascati
Daniele Marchionni, Telespazio
Raul Cafini, Telespazio
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2. EO Data Access Protocol - Summary
Status of the Document
Protocol Overview
Requirements Classes
Conformance Classes and ATS
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3. Status of the document 1/2
OGC Download Service for Earth Observation Products (DSEO) V /05/14
Single zip file delivered including:
The document: _Download_Service_for_Earth_Observation_Products.docx
The schema files:
dseo.xsd
metalink.xsd
Some examples XML files
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4. Status of the document 2/2
The document has been prepared following the latest template from OGC ( r4_New_OGC_Document_Template_Draft)
Requirement Classes provided in sections §9, §10
Conformance Classes & tests provided in section §11
The OGC doc ID has been reserved (13-043), but document not uploaded yet because waiting for SRR comments before posting
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5. DSEO Overview 1/2
The OGC Download Service For Earth Observation Products (DSEO) proposes as OGC Best Practice document the download protocol defined in ngEO project (described in [ngEO-DAGICD]).
The protocol supports the following scenarios:
The product is already available for download (on-line);
The product is under processing, but not ready yet (off-line / on-demand);
Additionally the following sub-cases are supported:
Product file available from multiple sources (parallel download);
The product is composed of multiple files, each possibly available from multiple sources (multiple download);
The product file is reachable via several HTTP redirections from the original URL.
Any combination of previous options.
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6. DSEO Overview 2/2 The DSEO protocol uses: DSEO service operations:
HTTP GET for all interactions;
HTTP redirections, in case of “virtual URL”;
Re-try mechanism according to specific HTTP returned codes, in case of on-demand products;
Metalink files for managing multi-file / multi-source download;
Key-Value Pairs (KVP) Encoding: the service operations receive parameters as list of key-value pairs in the request URL.
DSEO service operations:
GetCapabilities, in order to have compliance with OWS
GetProduct, the actual DSEO service operation
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7. DSEO Operations - GetCapabilities
GetCapabilities operation allows DSEO clients to retrieve the service metadata document from the server. This document specifies which operations can be invoked on the server, encodings, etc.
Request: it is a simple HTTP GET operation with KVP encoded parameters in the URL (service=DSEO, request=GetCapabilities, version=“1.0.0”, ...)
Example:
Response: the Capabilities XML document containing information about the service, supported operations, encodings, etc.
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8. DSEO Operations – GetProduct 1/3
GetProduct operation allows DSEO clients to request a particular EO product identified by a URI.
Request: it is a simple HTTP GET operation with KVP encoded parameters:
Service: Service type identifier
Request: Operation name
Version: Standard version for operation
ProductURI: URI of the product to be downloaded.
Example:
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9. DSEO Operations – GetProduct 2/3
GetProduct – Response:
Response Name
HTTP Status
Response type
MIME Type
Description
Direct Download
200 – Ok
Binary
application/octet-stream
Product data
Metalink Download
XML
application/metalink+xml
Metalink file (Metalink.xsd)
Partial Content
206 – Partial Content
Accepted Download
202 – Accepted
text/xml
dseo:ProductDownload Response (dseo.xsd)
Forwarded Download
303 – See Other
ASCII
text/html
See http specifications
Direct Download: single file on-line product;
Metalink Download: multi-file / multi-source on-line product (Multiple Download);
Partial Content: multi source file product (Parallel Download)
Accepted Download: off-line / on-demand download product;
Forwarded Download: external located product redirect information;
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10. DSEO Operations – GetProduct 3/3
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11. DSEO Requirement Classes
As OGC Best Practice, the document shall include Requirement Classes.
Requirement Classes:
Core, regrouping all requirements for supporting direct download, multi file download (Metalink), multi source download (Metalink), redirection.
On-demand Download, inheriting from Core class and including the requirements for allowing download of product files not ready yet.
In this way we cover: servers supporting only already available products (Core class) and also servers supporting on-demand products (Core + On-demand Download).
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12. DSEO Conformance Classes
Conformance Classes: Normally there is a 1:1 mapping between Requirement Classes and Conformance Classes, so we have:
Core (Conformance Class), regrouping all tests for verifying Core class requirements;
On-demand Download (Conformance Class), regrouping all tests for verifying On-demand Download class requirements.
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13. DSEO Conformance Tests
Conformance Tests: A conformance class is implemented via a set of conformance tests, each testing one or more requirements of the corresponding requirements class.
Core: contains the following conformance tests:
Capabilities
Capabilities request non-nominal conditions
Download of single file product
Download of multi-file product
Download of multi-source product
Redirected download of single file product
Product request non-nominal conditions
On-demand Download: contains the following conformance tests:
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14. DSEO Requirements Statistics
Requirement Class
Core: 14 Requirements
OnDemand: 2 Requirements
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15. DSEO Conformance Tests Statistics
Conformance Class
Core: 7 Conformance Tests
OnDemand: 4 Conformance Tests
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