ADS Web Services -- SOAP Prototypes

The promise of interoperability among platforms and languages and the availability of public-domain implementations for this protocol have contributed to the adoption of SOAP by astronomical data providers, among others. The ADS group, in the context of its collaboration with other NASA Data Centers, has started developing prototype SOAP services that can be used to query its search engine and other interfaces used to establish links among data centers.

This document describes two classes of services currently being prototyped:

External links management: a collection of SOAP services maintained by ADS collaborators which we use to create and validate links to them.
Query interface: SOAP services maintained by ADS providing access to its search engine, reference resolver and bibliographic code verification utilities.

External Links Management

In order to facilitate the creation of links to data providers and publishers, ADS has proposed two simple SOAP services described below:

Bibcode link server: a sample SOAP server (implemented as a CGI script) that outputs a list of records consisting of a bibcode, link URL, link descriptions (short and long), and link type. This type of service is used by ADS to harvest the data necessary to create links to each particular datacenter. By providing such an interface, each center can therefore "advertise" and maintain control over the links that ADS creates to it.
Dataset identifier verification server: a sample SOAP server (implemented as a CGI script) that takes an array of input dataset identifiers and checks to see if they are syntactically correct and known to the datacenter. For each input identifier, a record is returned indicating if the identifier is known, and if so it returns a URL and additional metadata that can be used to create a link to it.

The deployment of these services is currently very limited. For more information or if you are interested in providing these services, please contact us.

Query Interface

The prototype services we present here provide a SOAP interface to existing functionality that ADS has so far made available via the traditional HTML/HTTP/CGI user interfaces (Accomazzi et al. 1997) as well as through customized client-server interfaces (Eichhorn et al. 1996). Please note that currently access to these SOAP services is restricted. For more information on how to register to gain access to them, please contact us.

We tackled these services first since they are the ones that most of our collaborators use on a daily basis and because they expose the ADS search engine interface and our data holdings in a natural way. We have attempted to minimize the complexity of the data structures returned by the SOAP servers by adopting a simple representation for the bibliographic elements in our records. While this may fall short of the level of detail desired by some of our users, it greatly simplifies the amount of post-processing that client applications need to perform in order to create links to the ADS services.

The SOAP services implemented so far are described below.

Bibcode Verification: a service that verifies the existence of bibliographic records and returns their canonical bibcodes and URLs suitable for linking.
Reference Resolution: a service that requests the identification of free-text reference strings with their corresponding bibliographic records in ADS.
Abstract Query: a service that returns a list of records in the ADS abstract databases matching the input search parameters.

All of these scripts use the PERL module SOAP::Lite to send the properly encoded request to the ADS SOAP server. The server sends back a data structure that is accessible via the variable returned by $response->result. In the SOAP::Lite implementation, this corresponds to a reference to an array of hash references, which we serialize as an XML document via a call to XMLout, available from the XML::Simple PERL module.

We have implemented these SOAP prototypes in response to the suggestions and requests from other NASA Astrophysics Data Centers. Their deployment and the deployment of similar services by other data providers allows interested parties to test how usefully they can be integrated in distributed applications. Please keep in mind that the prototype services described here are just that: prototypes. They are not particularly efficient and should not to be used in production mode for the time being as their interface and service location is subject to change.

Please send all comments, bug reports and requests to Alberto Accomazzi, <aaccomazzi@cfa.harvard.edu> .