Friday, December 2, 2011

ql.io is interesting.

ql.io provides the same function as the ThumbWhere web service composition layer and was written to solve the same problem with the same philosophy of putting more control in the hands of developers.

Where it differs is that like YQL it is read-only so you can't compose everything.


What is a Web Service Composition Layer?

The aim is to push the back-and-forth traffic closer to the services and to avoid the return trip latency.

As developers one big constraint is the speed of light. To send a request, get the result, send another request based on the result, all this back and forth can add many seconds to the start up time of an application.

We can't make light go any faster, but we can make the total trip shorter.

If you need to make 6 calls to different systems to complete authentication, catalogue, entitlements and analytics, you are adding a lot to your client applications start up time.


Another aim to make sure that developers are not overly constrained by workflows imposed by services. You can be more granular with your services and know that the client can compose the workflow that suits the application or platform they are using. eg. PC vs Mobile can have radically different workflows for the same services.

  • As a service designer, you don't need to second guess every case that developers may come up with.
  • As a developer and service consumer, you can construct a perfect single web service call, every time.


ql.io combines JSON and SQL


I can appreciate that it is compact, but i'm concerned that it's hard to make existing web services look like tables in a database, and that for many front end developers SQL would be a new skill they would have to acquire,.


ThumbWhere's implementaion combines JavaScript and XPATH. This was carefully chosen to take advantage of the native XPATH engines that are available on the server side and in modern web browsers, XML/XPATH is at least a familiar technology to most front end developers.

In the environment where ThumbWhere was developed JavaScript and XSLT/XPATH was and is still a heavily used language for client side development, this was a consideration of the design.

(Here is the Composition layer being called from JavaScript).


Here it is being called from C#



Some features in ThumbWhere has that it's not obvious are in ql.io (site is down at the time of writing this article).

Asynchronous call backs: As the result streamed back from the server multiple call-backs can be triggered.

Generic feed integration (you can pull in any XML feed or existing REST web service call and manipulate it, use content as parameters for other calls in the composition).

Flow control (if/while) that allows a call to for example make decisions based on the return values of other.

Response Mutation: ThumbWhere lets you move, rename and delete elements of the feed or
API responses before they are sent back to the client.

Request Parallelisation: ThumbWhere can detect or lets you mark requests that can be run
in parallel.

Write & Execute: ql.io only has has a select statement (at this point). It's read only. Thumbwhere allows you to compose read and write operations.


What ql.io does provide is a wonderful join syntax and ability to perform complex reductions based on relations - which can be done using XPATH in ThumbWhere - but is not as nice as JOIN :)

If anything this is vindication for our approach.

Its a bit hard to try and induce a new way of thinking so I'm really glad that ql.io has put a stake in the ground for saner web services. With ql.io and YQL out there now, my elevator pitch will get less blank looks :)

I'm going to strongly consider rolling this into our notification/feed/edge stack as it's such a close fit with what we already have.


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