Post on 05-Jan-2016
description
transcript
Good Fences Make Good Neighbors1
Middleware for Aleph’s REST API
Rich Wenger, E-resource Systems Manager
MIT Libraries1. Frost, Robert. “Mending Wall” Collected Poems of Robert Frost. New York, Henry Holt and Co., 1930. 47. Print
Agenda
1. Short review of Aleph XML APIs
2. What is the API adapter?
3. Why did we build it?
4. Design criteria
5. How does it work?
6. Use cases
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Aleph XML APIs: X-server
1. http://walter.mit.edu/X?op=bor-info&library=mit50&bor_id=rwenger@mit.edu
2. http://walter.mit.edu/X?op=bor-by-key&bor_id=rwenger@mit.edu
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Aleph XML APIs: REST*
1. http://walter.mit.edu:1891/rest-dlf/patron/50481/circulationActions/loans
2. http://walter.mit.edu:1891/rest-dlf/patron/164423/circulationActions/cash
* REpresentational State Transfer - rest-web-services
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Aleph XML APIs
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AlephREST API External system
Standard access configuration
What is the API adapter?
1. A thin layer of programming between the Aleph REST API and external systems that use the API.
2. A Perl program that runs from Aleph’s cgi-bin directory.
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What is the API adapter?
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AlephREST API
External system
Adapter
Access configuration with adapter installed
Why did we build it?
To insulate Aleph and the calling system from each other, particularly in the case of a competing vendor. The software reflects the business model.
To provide an avenue for problem circumvention that does not depend on either Aleph or the calling system.
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Why did we build it?
To minimize the latency of network traffic by bringing multiple calls to the API inboard on the Aleph server instead of extending them across the network.
APIs change over time and between releases. An intermediate layer can mask such changes unless or until they prove useful.
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Why did we build it?
Simplifies access control. There is one place to whitelist external servers instead of multiple Aleph configuration files.
Provides the flexibility to augment Aleph data from other local systems if so desired.
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Design – the adapter should..
Integrate easily into the Aleph server environment.
Have a small footprint and be unobtrusive in its operation.
Return results ~identical to those generated by the Aleph REST API. before and after
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Design – the adapter should..
Not interfere in any way with the standard use of the Aleph REST API through the Tomcat/JBOSS server and port.
Consume Aleph REST API URL syntax without modification.
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Design – the adapter should..
Function in a transparent pass-through mode for all REST API services except for those intentionally modified by the host site.
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How does it work?
The adapter uses an Apache rewrite rule to direct REST URLs to itself running on port 80.
The external system sends its REST calls to port 80 instead of 1891.
The adapter parses the incoming URL and sends the request to the Aleph REST API via ‘localhost’.
Output from the REST API is passed back to the caller after any desired processing.
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Use case 1, ID translation
For patron functions, the REST API requires the patron’s Aleph id. Few, if any, authentication systems return an Aleph id as an identifier.
The REST API has no function to convert an alias to the corresponding Aleph id, but the X-server does.
This forces calling systems to use two calls across the network instead of one, and two different API’s.
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External System
Aleph server
JBOSS REST APIPort 1891
ApachePorts 80, 443
Calls to Aleph REST API without the adapter installed. Two calls.
X-serverAPI
http://walter.mit.edu/X?op=bor-by-key&bor_id=rwenger@mit.edu
50481 http://walter.mit.edu:1891/rest-dlf/patron/XML
External System
Aleph server
JBOSS REST APIPort 1891
ApachePorts 80, 443
Calls to Aleph REST API with the adapter installed in passive mode. Two calls.
X-serverAPI
http://walter.mit.edu/X?op=bor-by-key&bor_id=rwenger@mit.edu
50481 http://walter.mit.edu/rest-dlf/patron/XML
Adapter
External System
Calls to Aleph REST API with the adapter installed and using the X-server transparently. One call.
http://walter.mit.edu:1891/rest-dlf/patron/rwenger@mit.edu
XML
Aleph server
ApacheRewrite rule
AdapterJBOSS REST API
Port 1891X-serverAPI
Use case 2, data filtering
When using the adapter with the X-server.
The bor-info method returns historical data, including paid fines.
The adapter can filter paid fines from the response XML.
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Good Fences Make Good Neighbors
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AlephREST API
External system
Maintain control of the terrain where systems meet.
Useful Links
REST architecturehttp://www.slideshare.net/cebartling/rest-web-services
Aleph REST APIhttps://developers.exlibrisgroup.com/aleph/apis/Aleph-RESTful-APIs
Aleph X-serverhttps://developers.exlibrisgroup.com/aleph/apis/Aleph-X-Services
Ex Libris Developer Networkhttps://developers.exlibrisgroup.com/
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Finis
Rich Wenger rwenger@mit.edu
Phone 617-253-0035
Fax 617-253-4462
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