Re: [xml] How could I understand the slightly difference of the parsing process of E1/E2[E3] and E1[E2][E3]?
Thank you Bruce, I failed to find a good example to show how two interpretations would generate different outputs. They might always get the same results (either). I will read more and try to digest as you suggested. Thanks again, Ming From: Bruce Miller bruce.mil...@nist.gov To: Ming Chen ciming.c...@yahoo.com Cc: xml@gnome.org xml@gnome.org; Liam R E Quin l...@holoweb.net; mhy...@ustc.edu mhy...@ustc.edu Sent: Friday, January 20, 2012 10:14 PM Subject: Re: [xml] How could I understand the slightly difference of the parsing process of E1/E2[E3] and E1[E2][E3]? On 01/20/2012 12:46 AM, Ming Chen wrote: Thank you Bruce, My colleague began to have some approval of dealing a step (regardless of how many predicates attached) as a whole, //rec/(para[1]). That is a big progress for me. We are following the XPath 2.0 spec. Are the both have the same behaviour about the parsing of steps with predicates? Frankly, I haven't spent much time looking at the XPath 2 spec, since I would be wishing for features I can't use in my current applications... While we still cannot reach an agreement about the DFS and BFS dispute. For example, step1/step2/step3/step4, assume that each has multiple matched nodes, should it be interpreted as step1/(step2/(step3/step4)) or ((step1/step2)/step3)/step4? Either, depending on what you mean by the parentheses : You might try the XPath 1 spec as (possibly) being shorter and easier to digest; especially section 2 about Location Paths: The initial sequence of steps selects a set of nodes relative to a context node. Each node in that set is used as a context node for the following step. The sets of nodes identified by that step are unioned together. Hope that helps; bruce ___ xml mailing list, project page http://xmlsoft.org/ xml@gnome.org http://mail.gnome.org/mailman/listinfo/xml
Re: [xml] How could I understand the slightly difference of the parsing process of E1/E2[E3] and E1[E2][E3]?
On 01/20/2012 12:46 AM, Ming Chen wrote: Thank you Bruce, My colleague began to have some approval of dealing a step (regardless of how many predicates attached) as a whole, //rec/(para[1]). That is a big progress for me. We are following the XPath 2.0 spec. Are the both have the same behaviour about the parsing of steps with predicates? Frankly, I haven't spent much time looking at the XPath 2 spec, since I would be wishing for features I can't use in my current applications... While we still cannot reach an agreement about the DFS and BFS dispute. For example, step1/step2/step3/step4, assume that each has multiple matched nodes, should it be interpreted as step1/(step2/(step3/step4)) or ((step1/step2)/step3)/step4? Either, depending on what you mean by the parentheses : You might try the XPath 1 spec as (possibly) being shorter and easier to digest; especially section 2 about Location Paths: The initial sequence of steps selects a set of nodes relative to a context node. Each node in that set is used as a context node for the following step. The sets of nodes identified by that step are unioned together. Hope that helps; bruce ___ xml mailing list, project page http://xmlsoft.org/ xml@gnome.org http://mail.gnome.org/mailman/listinfo/xml
Re: [xml] How could I understand the slightly difference of the parsing process of E1/E2[E3] and E1[E2][E3]?
Thank you Bruce, My colleague began to have some approval of dealing a step (regardless of how many predicates attached) as a whole, //rec/(para[1]). That is a big progress for me. We are following the XPath 2.0 spec. Are the both have the same behaviour about the parsing of steps with predicates? While we still cannot reach an agreement about the DFS and BFS dispute. For example, step1/step2/step3/step4, assume that each has multiple matched nodes, should it be interpreted as step1/(step2/(step3/step4)) or ((step1/step2)/step3)/step4? Thanks, Ming From: Bruce R Miller bruce.mil...@nist.gov To: Ming Chen ciming.c...@yahoo.com Cc: xml@gnome.org xml@gnome.org; Liam R E Quin l...@holoweb.net Sent: Friday, January 20, 2012 4:49 AM Subject: Re: [xml] How could I understand the slightly difference of the parsing process of E1/E2[E3] and E1[E2][E3]? Ming Chen wrote: Hi Experts, Recently a colleague and I have disagreed on the parsing process of the E1/E2[E3], where E3 has a numeric type. Here is the example XML file: ?xml version=1.0 encoding=UTF-8? xml table rec id=1 para type=error position=11/ para type=warning position=12/ para type=warning position=13/ /rec rec id=2 para type=warning position=21/ para type=warning position=22/ para type=warning position=23/ /rec rec id=3 para type=info position=31/ para type=warning position=32/ para type=warning position=33/ /rec /table /xml For XPath expression //rec/para[1], xmllint.exe outputs: para type=error position=11/para type=warning position=21/para type=info position=31/ While my colleague said that the output should be: para type=error position=11/ Your colleague is is interpreting the xpath expression as ( //rec/para ) [1] rather than //rec / (para[1]) See section 2.1 of the XPath (1.0) spec; The predicate, in this case [1], is part of the step. So //rec selects a set of rec nodes, then for each, the next step para[1] is applied and the union is formed. Not that the predicate [1] is applied to the union. ... So, what's the nice distinction between E1/E2[E3] and E1[E2][E3]. The first xpath has 2 steps, where the 2nd step has one predicate. The second xpath has 1 step which has 2 predicates. When there are multiple predicates, they are applied left to right as if they were successive filters.___ xml mailing list, project page http://xmlsoft.org/ xml@gnome.org http://mail.gnome.org/mailman/listinfo/xml
[xml] How could I understand the slightly difference of the parsing process of E1/E2[E3] and E1[E2][E3]?
Hi Experts, Recently a colleague and I have disagreed on the parsing process of the E1/E2[E3], where E3 has a numeric type. Here is the example XML file: ?xml version=1.0 encoding=UTF-8? xml table rec id=1 para type=error position=11/ para type=warning position=12/ para type=warning position=13/ /rec rec id=2 para type=warning position=21/ para type=warning position=22/ para type=warning position=23/ /rec rec id=3 para type=info position=31/ para type=warning position=32/ para type=warning position=33/ /rec /table /xml For XPath expression //rec/para[1], xmllint.exe outputs: para type=error position=11/para type=warning position=21/para type=info position=31/ While my colleague said that the output should be: para type=error position=11/ According to his explaination, only after all evaluations of E2 against all nodes resulting from the evaluation of E1, the evaluation of E3 can begin. As for the example, the process looks like: rec(id = 1) - all para under rec (id = 1) - rec(id = 2) - all para under rec (id = 2) - rec(id = 3) - all para under rec (id = 3) , the result sequence then acts as the input sequence of the evaluation of E3, so only the very first para node should be ouput. To me, this is a little bit like BFS (Breadth-First-Search). On the contrary, I think the process should be: rec(id = 1) - all para under rec (id = 1) - get the first para under rec (id = 1) - rec(id = 2) - all para under rec (id = 2) - get the first para under rec (id = 2) - rec(id = 3) - all para under rec (id = 3) - get the first para under rec (id = 3). The first para node under each rec should be output, as xmllint.exe did above. Could be regarded as DFS (Depth-First-Search)? I havn't found a clear definition about the parsing rule from the XPath spec. Or you can say that I have not understood the spec well :). Anyway, I cannot persuade him even I have shown him many XML tools that really performs the same with xmllint.exe. Could someone give me the theoretical support? My colleague used another XPath expression to support his opinion: //rec[1]/para[@type=warning][2] (Please focus on the latter part: para[@type=warning][2], I purposely used rec[1] to avoid mix-up). In this case, all evaluations of E2 against all nodes resulting from the evaluation of E1 have been done before the evaluation of E3. The output of para[@type=warning] act as the input sequence of E3. Sounds reasonable? BFS? As descibed in section 3.3.2 Predicates of XPath spec 2.0 (1.0 should follow it too): In the case of multiple adjacent predicates, the predicates are applied from left to right, and the result of applying each predicate serves as the input sequence for the following predicate. So, what's the nice distinction between E1/E2[E3] and E1[E2][E3]. They both evaluate using inner focus, a paragraph of the spec lists both together as if they completely consistent (but do they really follow the same parsing rule?): Cited from 2.1.2 Dynamic Context (Spec 2.0): Certain language constructs, notably the path expression E1/E2 and the predicate E1[E2], create a new focus for the evaluation of a sub-expression. In these constructs, E2 is evaluated once for each item in the sequence that results from evaluating E1. Each time E2 is evaluated, it is evaluated with a different focus. The focus for evaluating E2 is referred to below as the inner focus, while the focus for evaluatingE1 is referred to as the outer focus. The inner focus exists only while E2 is being evaluated. When this evaluation is complete, evaluation of the containing expression continues with its original focus unchanged. Any commens would be appreciated. Hi Liam, Could you have a look at this :) Thanks, Ming ___ xml mailing list, project page http://xmlsoft.org/ xml@gnome.org http://mail.gnome.org/mailman/listinfo/xml
