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Web Services at CBS: development


The work on SOAP based Web Services at CBS is done within the framework of EMBRACE Network of Excellence.

Currently CBS offers around 50 services on the WWW, including whole genome visualization and analysis, gene finding and analysis of DNA microarray data alongside predictions of protein sorting, post-translational modifications, structure and function. The services are currently available as traditional paste-and-click (interactive) HTML forms. Following the EMBRACE technology recommendations we are in the process of implementing them as Web Services proper. The activities involve the following:

  1. Development of an environment for implementing SOAP based Web Services on the server side;
  2. Implementation of individual services (main task);
  3. Development of client side solutions aiming at using Web Services in practice;
  4. Work on Web Service interoperability and data type integration.
Below we describe the activities above in greater detail. Specifically, we describe the current status of the work and outline the future plans.

1. Server side environment

We have developed a stable environment for implementing SOAP based Web Services on the server side. The implementation is in Perl/SOAP::Lite. It features easy-to-customize template scripts, a queue and a logging function. It allows for asynchronous calls when that is preferable. Most services implemented so far are fully asynchronous; typically, the usage is split into the three operations 'runService', 'pollQueue' and 'fetchResult'. All the services are described in documented WSDL files; they have been tested with SoapUI, Perl/SOAP::Lite and Python/SOAPpy scripts on the client side.

The key implementation decisions have been as follows:

  • Technology: the choice of Perl/SOAP::Lite has been purely pragmatic, reflecting the existing programming skills in our lab. We are aware of the existence of alternative technologies. Still, we found that using Perl/SOAP::Lite we were able to implement stable services with a reasonable effort.

  • Asynchronous calls: this was necessary to implement as most of our services are computationally demanding. The response is seldom immediate. In the absence of commonly accepted standard we have developed a simple scheme (see above). This approach is in agreement with the EMBRACE technology recommendations, pending a common standard for asynchronous calls.

2. Implementation of individual services

The complete list of the electronic services at CBS is provided on the prediction servers and bioinformatics tools pages. All the services are currently implemented as traditional paste-and-click (interactive) HTML forms. The effort to implement them as SOAP based Web Services is in progress.

We intend to make the corresponding Web Services easy to understand and use. To that end we have given special consideration to the following issues:

  • Extensive and easy-to-find documentation
    The Web Services implemented so far are available from the CBS Web Services page. Each Web Service has its own WWW page (e.g. http://www.cbs.dtu.dk/ws/SignalP) where the basic information about the service can be found:
          - service name and basic function;
          - link to the WSDL file defining the service;
          - list of links to the schema definitions used by the service;
          - examples of client side scripts (PERL, PYTHON) using the service;
          - documentation (identical to the documentation found in the WSDL file).

  • Suitable extent of implementation
    Typically the implemented services offer the same functionality as their paste-and-click counterparts. However, we have focused on the scientific content of the output and limited the generation of graphics, extended formats etc. We believe that our Web Services will be used for efficient automatic processing of large amounts of data. The clients with special interests e.g. just one protein or a few genes are likely to prefer the traditional paste-and-click services for detailed study. This policy may change if we receive comments from users pointing to the contrary.

  • Easiness of parsing
    The programming effort involved in parsing the output of a Web Service is greatly reduced if it is structured i.e. expressed in strictly defined data types. Therefore, in most cases we have chosen to produce strongly typed output in an easy-to-access form making it convenient to integrate with local routines and other Web Services. In fact, the WP3 recommendations discourage loose data typing as it weakens the advantages of the selected technology. The matter is discussed in greater detail in our comments on implementation strategy.
The setup described above is quite new; we are very grateful for comments and improvment suggestions. The effort is in progress; the setup is being refined and more services are being added. The order in which this is done depends very much on user feedback.

3. Client side solutions

Our effort on the client side focuses on development of scripts and programs calling SOAP based Web Services. Such scripts can be executed directly from the command line or included in larger softwares, increasing the local bioinformatics toolbox dramatically with a limited programming effort. The operations of any Web Service, local or remote, are easily turned into functions (subroutines) in the scripts and programmes created locally. We feel that this approach makes the best of the Web Service technology and its power to provide a truly integrated data and tool environment. We see client side scripting as a useful supplement to the existing and emerging graphical interfaces to Web Services.

The key implementation decision on the client side was the choice of language. Perl was the obvious starting point as the server side work was done in that language. However, we have discovered that the Web Services support in Python is much better; the object oriented features of Python agree very well with Web Services. Although the commonly used Python module SOAPpy suffers from lack of updates (most recent version 0.12 is from Feb 2005), we are in the process of supplementing our Perl client scripts with Python counterparts using this module.

On Feb 6-8, 2008 CBS will host an EMBRACE workshop on Client Side Scripting for Web Services. The workshop will focus on practical use of Web Services in scripts and programs developed on the user's own computer. There will be several hands-on exercises; the general concepts involved in calling Web Services from a script will be explained in detail. On-line registration is currently open with the deadline on December 3, 2007.

On Jan 24-26, 2007 CBS organized an EMBRACE workshop on Bioinformatics of Immunology. During the workshop exercises the participants were given opportunity to develop client side WS scripts in Perl. For convenience, the exercise cookbooks and script examples remain on-line, linked from the workshop program.

4. Web Service interoperability and data type integration

Client side applications often need to use the output of one Web Service as input to another. If the data types match the task of linking Web Services becomes straightforward. If they do not match it is still possible but it requires additional programming effort, slowing down the software development. If the Web Services involved operate on untyped data the client's programming effort is even greater. Therefore, we are strong advocates of strictly typed Web Services and standard data types.

In our own implementation effort we have tried to reuse data types whenever possible. We have defined a number of data types of general validity (see examples). We intend to use those data types consistently in our Web Services, simplifying implementation and usage. We address Web Service interoperability in greater detail in our comments on implementation strategy.

Acknowledgements

Thanks are due to Jan Christian Bryne at Computational Biology Unit (CBU) in Bergen, Norway who organised a workshop on Web Services in May 2006. On that workshop we gained the initial understanding of SOAP based Web Services and charted the implementation possibilities.

We also attended the joint EMBRACE Work Package 1 and 2 workshop at EBI in Hinxton, UK in June 2006. We are grateful to Peter Rice and Alan Bleasby for leading the discussions that allowed us to define the main issues to be addressed in our own implementation effort.

Pall Isolfur Olason created the first prototype Web Services at CBS. In the current effort we benefited greatly from his experience and help.




CONTACT

Kristoffer Rapacki,