Yossi Dahan [BizTalk]

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Thursday, December 27, 2007

Mapper vs. XSLT round 2


I've received a good question today -

"we had a little debate in the office today - what is faster - running a map with pure xsl or the standard way with functoids, what you think?"

As I've
blogged before - I'm a big supporter of writing custom XSL and not using the Mapper and Functoids in anything other than the simplest of maps; so - although performance is only one of my arguments - the answer should be obvious.

Nevertheless I'll take the chance to answer properly again, although I suspect the question is not accurate enough -

At runtime there's no difference between the two; the Mapper generates XSL (which you can see by "validating" the map in visual studio and following the link to the XSL file generated which would appear in the output window, so the question should be, in my view, whether the Mapper can generate as good XSL as a developer could, but as you can imagine the answer really depends on a particular scenario - how many functoids are you using? how are they working together? what's the size of the map? what's its complexity?

Anyway, in my view there is a bottom line answer to that question and that is that under most real-world scenarios custom written XSL will almost always be better than generated one, but I'll try to explain a little bit more -

When you're using Functoids in your map you're generally doing one of two things - you're either calling external assemblies or you're adding some XSL lines to perform some actions for you.

The former one is easier to tackle - if you need external assemblies you can call them from custom XSL as well (as I've explained
here ); as the Mapper will do exactly the same, the performance impact will generally be identical in both cases (using mapper or custom XSL).

The latter is harder to tackle, as there's no one-rule-fits-all statement one can make - but here's a shot at it -

The Mapper is a visual, generic, designer that generates code.
As is always the case with these tools they come with a price, and that price is often the quality of the code generated; now - don't get me wrong - I don't argue that the Mapper is bad, or that it always generates bad, slow XSL; but if you know XSL well, there's no doubt you will write better code than a generator will.

When you're adding a Functoid that does not call an external assembly you'll be doing one of three things -

  • You will be adding an embedded c# code - most Functoids do this, look at the string manipulations as a simple example.

  • You will be adding a template based on input nodes - the Looping Functoid for example.

  • Or - You will be adding XLS structures or functions - the record count or value mapping Functoids for example


  • All three are perfectly fine, and even more so - if you'll try them out you'll see that the designer does generate quite a nice XLS in all cases.

    The problem starts when, and this is inevitable in the real-world, the maps get more complex.

    Once you move out of the playing ground and into real scenarios, the maps get more complicated and the inefficiency of the generated code becomes both more apparent (as multiple Functoids need to work together to achieve the desired output the XSL gets 'uglier and uglier') and that inefficiency becomes a greater problem as it is repeated many times over a large-ish map.

    Bottom line is from my perspective - if you feel comfortable with XSL (and the rest of the team) - you will always achieve better scripts than any generator would so use it. If you don't feel comfortable with XSL - learn it! It's easy! (and in the mean time use the mapper).

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