How to model logical/boolean expressions in XML efficiently?

Little xml modeling exercise here. Let's say we have some logical expression: (x & y) | (p & q) and it needs to be expressed in XML for whatever reason. Here is a quick stab, but I think this is clumsy:

    x y  p q

Another stab, which doesn't smell right to me: How would you go about it? asked Apr 6, 2012 at 21:53 8,333 18 18 gold badges 81 81 silver badges 149 149 bronze badges

4 Answers 4

Armatus answer looks good to me. I consider the left and right element as redundant. Having a logical expression it doesn't matter if i evaluate them left right or right left.

   x y  p q

for example: (x & y) | (p & q) is the same as (q & p) | (y & x)

furthermore its possible to add more than just two signals.

2,881 9 9 gold badges 35 35 silver badges 37 37 bronze badges answered Feb 10, 2014 at 10:07 813 9 9 silver badges 14 14 bronze badges

For > or < left and right would be important. IMHO being able to "group" more than one signal is a nice convenience feature, but they would still have to be processed two at a time.

Commented Sep 10, 2018 at 6:38

   xy    pq

answered Apr 6, 2012 at 22:11 2,191 17 17 silver badges 28 28 bronze badges that is nicely consistent and nestable. Commented Apr 6, 2012 at 22:20 Instead of the : you could also use a type attribute ( type="or" etc.). Commented Apr 6, 2012 at 22:27

Your first "quick stab" looks perfectly reasonable to me, except perhaps for the outer 'expr' element, which doesn't add much value.

answered Apr 6, 2012 at 22:36 Michael Kay Michael Kay 162k 11 11 gold badges 94 94 silver badges 169 169 bronze badges

It's interesting to look at how expression trees are modeled in Microsoft .NET's System.Linq.Expressions namespace. The basic concept that I think is important here, is that everything inherits from the basic Expression class – so pretty much everything is an expression, be it a binary operation, a parameter, a constant, .. etc.

Furthermore, the NuGet package Serialize.Linq demonstrates how such expression trees could be serialized to XML for example.

Long solution

That's just for reference though. I think the XML model can be made even simpler. I would model your example like this:

       x y  p q

Short solution

Depending on your implementation, you might be able to omit the element and type attributes and handle those things in a more "implicit" way when interpreting the expression (kind of like JavaScript, PowerShell, . ). Also, you could make the element and type names shorter, if the size/length of the XML output is an issue.

So, here is a and example of a highly shortened version:

  x y  p y

Another example

For the sake of completeness, here another example of how a more complex expression would be modeled in such a way.

Pseudo code lambda/arrow expression:

(float b, int e) => e == 0 ? 1 : (e == 1 ? b : pow(b, e))

      e 0  1  e 1  b  p e