XPath with Multiple Predicates

[Eldon Carman <ec...@ucr.edu>]

I have a XML data source that I could filter with two XPath
predicates. Does MRQL support this type of XPath expression?

For example: [f='foo' and b='bar']

Re: XPath with Multiple Predicates

[Leonidas Fegaras <fe...@cse.uta.edu>]

Hi Eldon,
MRQL doesn't contain XPath. It can simulate XML paths but the rest are 
done using select queries.

 From http://wiki.apache.org/mrql/LanguageDescription:

MRQL also provides syntax to navigate through XML data. The projection 
operation e.A has been overloaded to work on XML data. Given an 
expression e of type XML or list(XML), e.A returns a list(XML) that 
contains the subelements of e with tagname A (much like e/A in XPath). 
Similarly, the syntax e.*, e.@A, and e.@* correspond to the XPaths e/*, 
e/@A, and e/@*, respectively.

You can simulate XPath predicates using predicates in select queries:

select text(a.title)
  from a in source(xml,"dblp.xml",{"incollection"})
where text(a.author) = "Daniel Brandon" and text(a.year) = "2005";

which is equivalent to the XPath:
//incollection[author = "Daniel Brandon" and year = "2005"]/title

Leonidas



On 06/13/2014 02:40 AM, Eldon Carman wrote:
> I have a XML data source that I could filter with two XPath
> predicates. Does MRQL support this type of XPath expression?
>
> For example: [f='foo' and b='bar']