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HTRC Data API Users Guide

Version Status Maturity Comments
1.0 Released Released  
1.0.1-SNAPSHOT Under testing Release candidate Added token count feature

 

 

 

Synopsis

API

Response Format

Access Data API with OAuth2

Synopsis

The HTRC Data API is a RESTful web service for the retrieval of multiple volumes, pages of volumes, and METS metadata documents.  In order to support the efficient retrieval of volumes and pages in bulk, the Data API deviates from the typical RESTful API design out of necessity in that resources are not identified on the URL paths, but instead are sent as request parameters.

In version 1.0.1 of the Data API, it adds a feature allowing client to request for token counts of volumes.

API

Note: all parameter values must be URL encoded

Retrieve Volumes

Description Returns requested volumes
URL  /volumes
 Supported Response Types

application/zip (normal response)

text/plain (error response)

 Method  POST
 Request Types  application/x-www-form-urlencoded
 Request Headers  Content-Type: application/x-www-form-urlencoded
 Request Body  Request parameters as body content.  See Parameters below
 Parameters
Name Description Type Default Value  Required Note
 volumeIDs  The list of volumeIDs to be retrieved.  string  N/A  yes  VolumeIDs are separated by the pipe character '|'
 mets  The flag to indicate if METS document should be returned  boolean  false  no  
 concat  The flag to indicate concatenation option.  boolean  false  no  See section on response format for details on its impact on the returned data
 version  A specific version of the Data API to use  string  N/A  no  Not implemented.  Place holder only 
 Responses
HTTP Status Code Response Body Response Type Description
 200 (ok)  A binary Zip stream  application/zip  Page content and metadata of the requested volumes aggregated as a Zip stream
 400 (bad request)  Missing required parameter volumeIDs  text/plain  The required parameter volumeIDs is missing in the request
 400 (bad request)  Malformed Volume ID List. Offending token: ${token}  text/plain The value for volumeIDs is malformed and the Data API cannot parse it.  ${token} will be the token that causes the error. 
 Example
Description Request for volumes inu.3011012 and uc2.ark:/13960/t2qxv15, with concatenation option enabled so each volume is a single text file in the returned Zip stream.
raw volumeIDs inu.3011012|uc2.ark:/13960/t2qxv15
URL encoded request body volumeIDs=inu.3011012%7Cuc2.ark%3A%2F13960%2Ft2qxv15&concat=true

 

Retrieve Pages

Description Returns requested pages
URL /pages
Supported Response Types

application/zip (normal response)

text/plain (error response)

Method  POST
Request Types  application/x-www-form-urlencoded
Requset Headers  Content-Type: application/x-www-form-urlencoded
Request Body  Request parameters as body content.  See Parameters below
Parameters
Name Description Type Default Value Required Note
 pageIDs  The list of pageIDs to be retrieved  string  N/A  yes  PageIDs are separated by the pipe character '|'
 concat  The flag to indicate concatenation option  boolean  false  no

 See section on response format for details on its impact on the returned data

*"concat" and "mets" cannot be both set

 mets  The flag to indicate if METS documents should be returned  boolean  false  no *"concat" and "mets" cannot be both set
 version  A specific version of the Data API to use  string  N/A  no  Not implemented.  Place holder only 
Responses
HTTP Status Code Response Body Response Type Description
 200 (ok)  A binary Zip stream  application/zip Page content and metadata of the requested pages aggregated as a Zip stream 
 400 (bad request)  Missing required parameter pageIDs  text/plain  The required parameter pageIDs is missing in the request
 400 (bad request)

 Malformed Page ID List.

Offending token: ${token}

 text/plain  The value for pageIDs is malformed and the Data API cannot parse it.  ${token} will be the token that caused the error.
 400 (bad request)  Conflicting parameters in page retrieval. Offending Parameters: ${param1}, ${param2}  text/plain Some request parameters have conflict. ${param1} and ${param2} will be the names of the parameters that caused the conflict. In the current version of the Data API, this is most likely caused by setting both "mets" and "concat" for page retrieval. 
Example
Description Request for the 1st, 2nd, 20th, and 30th pages of the volume inu.3011012, and the 11th, 17th, 22th, 30th, 45th, and 55th pages of the volume uc2.ark:/13960/t2qxv15, with each page being a separate text file along with the corresponding METS document of each volume in the returned Zip stream. 
 Raw pageIDs  inu.3011012[1,2,20,30]|uc2.ark:/13960/t2qxv15[11,45,30,17,22,55]
 URL encoded request body  pageIDs=inu.3011012%5B1%2C2%2C20%2C30%5D%7Cuc2.ark%3A%2F13960%2Ft2qxv15%5B11%2C45%2C30%2C17%2C22%2C55%5D&mets=true

 

Token Count

Description Returns token counts of requested volumes
URL /tokencount
Supported Response Types

application/zip (normal response)

text/plain (error response)

Method POST
Request Types application/x-www-form-urlencoded
Request Headers Content-Type: application/x-www-form-urlencoded
Request Body Request parameters as body content.  See Parameters below
Parameters
Name Description Type Default Value  Required Note
 volumeIDs  the list of volumes to be token counted string  N/A  yes  VolumeIDs are separated by the pipe character '|'
 level  specifies whether the token counts to be aggregated at volume level or page level.  Use "volume" for volume level, and "page" for page level string   volume  no  
 sortBy  specifies the token count output to be sorted on a fields. Use "token" for sorting based on the token's UTF-8 order, and "count" for sorting based on the token count order.  If left unspecified, the results do not guarantee any orders. string  N/A  no Token ordering is based on UTF-8 character values, so character "Z" comes before character "a" (if using ascending ordering).  For token count ordering, tokens with the same count are ordered by token's UTF-8 values. 
 sortOrder  specifies whether output to use ascending or descending ordering.  Use "asc" for ascending ordering, and "desc" for descending ordering. string  asc  no  this parameter only has effect when used together with sortBy, otherwise it is ignored.
 version  A specific version of the Data API to use string   N/A  no  Not implemented.  Place holder only
Responses
HTTP status code Response Body  Response Type  Description
 200 (ok)  a binary Zip Stream  application/zip  Token count output aggregated as a Zip stream
 400 (bad request)  Missing required parameter volumeIDs  text/plain  The required parameter volumeIDs is missing in the request
 400 (bad request)

 Malformed Volume ID List.

 Offending token: ${token}

 text/plain   The value for volumeIDs is malformed and the Data API cannot parse it. ${token} will be the token that caused the error. 
Example
Description  Request for page level token count of the volumes inu.3011012 and uc2.ark:/13960/t2qxv15, with the token count output to be sorted by the tokens in descending order
Raw volumeIDs  inu.3011012|uc2.ark:/13960/t2qxv15
 URL encoded request body  volumeIDs=inu.3011012%7Cuc2.ark%3A%2F13960%2Ft2qxv15&level=page&sortBy=token&sortOrder=desc

 

Response Format

Zip Structure Layout

The directory structure layout of the Zip stream returned from the Data API may be one of the following patterns depending on the optional parameters:

Strictly speaking, inside a Zip file the structure is flat, so there is no "directories" but only file entries.  However, in practice almost all Zip tools give the illusion of directories by leveraging the slash characters '/' in the name of each Zip entry.  For the discussion here, we follow such practice and treat the inside of a Zip file as if it were a conventional filesystem.

Suppose there are 2 hypothetical volumes in the corpus: foo.001122, which has 5 pages, and bar.ark:/13960/t123, which has 3 pages.  Both volumes also have the associated METS xml files.  The client tries to request for these 2 volumes, and also tries to request for another volume gon.000000 that no longer exists in the corpus, which would cause the entry ERROR.err to be included in the returned Zip strea.

Request Description Zip Structure Layout Explanation of Entries

Retrieve volumes

concat=false

volumes.zip

    |-- foo.001122/

    |    |-- 00000001.txt

    |    |-- 00000002.txt

    |    |-- 00000003.txt

    |    |-- 00000004.txt

    |    |-- 00000005.txt

    |    \-- mets.xml

    |-- bar.ark+=13960=t123/

    |    |-- 00000001.txt

    |    |-- 00000002.txt

    |    |-- 00000003.txt

    |    \-- mets.xml

    \-- ERROR.err

Because the request parameter concat=false, each volume has its own directory, and the pages and metadata documents of each volume are individual files stored under the volume directory.

foo.001122/ is a directory named after the first volume, foo.001122.  The directory name underwent a Pairtree clean process, but since it does not contain any filesystem unsafe characters, the cleaned ID looks the same as the original.

Inside foo.001122/, files 00000001.txt through 00000005.txt are the 5 pages of this volume

mets.xml will also be inside of foo.001122/ if the request parameter mets=true

bar.ark+=13960=t123/ is a directory named after the second volume, bar.ark:/13960/t123.  The directory name underwent a Pairtree clean process so that filesystem-unsafe characters such as colons ':' and slashes '/' are escaped and replaced with filesystem-safe characters.

Inside bar.ark+=13960=t123/, files 00000001.txt through 00000003.txt are the 3 pages of this volume.

mets.xml will also be inside of bar.ark+=13960=t123/ if the request parameter mets=true

ERROR.err is a file at the top level.  It is present if the request encountered some errors and the detailed error information is stored in this file.  In this example, its presence is caused by the request for a non-existent volume gon.000000

Retrieve volumes

concat=true

volumes.zip

    |-- foo.001122.txt

    |-- foo.001122.mets.xml

    |-- bar.ark+=13960=t123.txt

    |-- bar.ark+=13960=t123.mets.xml

    \-- ERROR.err

Because the request parameter concat=true, each volume is a single text file, where the pages of the volume are concatenated into the file in the page order.

foo.001122.txt is the text file entry for the volume foo.001122.  The filename underwent a Pairtree clean process, but since it does not contain any filesystem unsafe characters, the cleaned ID looks identical to the original.

foo.001122.mets.xml will be present if the request parameter mets=true.

bar.ark+=13960=t123.txt is the text file entry for the volume bar.ark:/13960/t123.  The filename underwent a Pairtree clean process, so filesystem-unsafe characters such as colons ':' and slashes '/' are replaced with filesystem-safe characters.

bar.ark+=13960=t123.mets.xml will be present if the request parameter mets=true.

ERROR.err is a file at the top level.  It is present if the request encountered some errors and the detailed error information is stored in this file.  In this example, its presence is caused by the request for a non-existent volume gon.000000

Retrieve pages

concat=false

pages.zip

    |-- foo.001122/

    |    |-- 00000001.txt

    |    |-- 00000002.txt

    |    |-- 00000003.txt

    |    |-- 00000004.txt

    |    |-- 00000005.txt

    |    \-- mets.xml

    |-- bar.ark+=13960=t123/

    |    |-- 00000001.txt

    |    |-- 00000002.txt

    |    |-- 00000003.txt

    |    \-- mets.xml

    \-- ERROR.err

The Zip stream returned from the Data API for page retrieval with the request parameter concat=false is very similar to that returned for volume retrieval with concat=false.  The difference is that only pages requested for will be included. 

 Retrieve pages

 concat=true

 pages.zip

    |-- wordseq.txt

    \-- ERROR.err

Because the request parameter concat=true, the returned Zip stream is a "sequence of words" where the content of all pages from all volumes is aggregated into a single text file entry named wordseq.txt.

ERROR.err is a file at the top level.  It is present if the request encountered some errors and the detailed error information is stored in this file.  In this example, its presence is caused by the request for a non-existent volume gon.000000

Note that there is no METS metadata returned because mixing METS metadata and page content into the word sequence could potentially contaminate the information in the word sequence file. 

 Token count

level=volume

 tokencount.zip

    |-- foo.001122.count

    |-- bar.ark+=13960=t123.count

    \-- ERROR.err

Because the request parameter level=volume, the returned Zip stream contains the token count of each volume as an entry, and the name of the entry is the Pairtree cleaned volumeID with ".count" as the extension.

 ERROR.err is a file at the top level.  It is present if the request encountered some errors and the detailed error information is stored in this file.  In this example, its presence is caused by the request for a non-existent volume gon.000000

 Token count

level=page

tokencount.zip

    |-- foo.001122/

    |    |-- 00000001.count

    |    |-- 00000002.count

    |    |-- 00000003.count

    |    |-- 00000004.count
    |    \-- 00000005.count

    |-- bar.ark+=13960=t123/

    |    |-- 00000001.count

    |    |-- 00000002.count

    |    \-- 00000003.count

    \-- ERROR.err 

Because the request parameter level= page, in the returned Zip stream, each volume is a directory whose entry name is the Pairtree cleaned volumeID, and each page of the volume is an entry under the directory, and the name of the page is the 8-digit zero-padded page sequence number followed by ".count" extension.

ERROR.err is a file at the top level.  It is present if the request encountered some errors and the detailed error information is stored in this file.  In this example, its presence is caused by the request for a non-existent volume gon.000000 

 

Token Count Output Format and Sorting Order

Each token count output entry is a list of tokens and number of occurrences within the aggregation.  The token and its occurrence count is separated by a space character (0x20), and each token-occurrence pair is a line and is separated from other pairs by a new line character (0x0A).  However, if an aggregation does not contain any texts (e.g. an empty page), that particular entry will be empty.

sortBy & sortOrder Token Count Output Description
unspecified

orange 1

banana 2

acorn 2

A-team 1

Xylophone 3

apple 1

coconut 1

if the parameter sortBy is not specified, the returned result does not guarantee any ordering of the token-occurrence pairs, nor does it guarantee the same ordering of these pairs between any 2 runs with the exact same parameters
sortBy=token&sortOrder=asc

A-team 1

Xylophone 3

acorn 2

apple 1

banana 2

coconut 1

orange 1

with ascending ordering on the tokens, the returned result is sorted using the UTF-8 value of the tokens in ascending order.  In this example, the tokens starting with capital letter "X" come before these starting with lower case letter "a".
sortBy=token&sortOrder=desc

orange 1

coconut 1

banana 2

apple 1

acorn 2

Xylophone 3

A-team 1

this is the exact reverse of the case above
sortBy=count&sortOrder=asc

A-team 1

apple 1

coconut 1

orange 1

acorn 2

banana 2

Xylophone 3

with ascending ordering on the occurrence count, the returned result is sorted using the count value in ascending order; however, when multiple tokens have the same count, the order is determined by the ascending ordering of the tokens.
sortBy=count&sortOrder=desc

Xylophone 3

banana 2

acorn 2

coconut 1

apple 1

A-team 1

this is the exact reverse of the above case, and specifically, when multiple tokens have the same count, the order is determined by the descending ordering of the tokens.

 

Access Data API with OAuth2

While the Data API by itself does not enforce any security mechanism for authentication and/or authorization, it is typically deployed behind an OAuth2 Servlet Filter.  A client making request to the Data API through the OAuth2 Servlet Filter must first obtain a valid OAuth2 token from the token service, and present the token as an additional HTTP request header to the OAuth2 Servlet Filtered Data API.  Please refer to " Using WSO2 Identity Server as the OAuth2 Provider for HTRC" for details on the usage.