[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Concerned about the increasing reliance on XPath
" If I write an application that will process an XML vocabulary and that can contain XPath then my application must implement the entire XPath specification" Only if you use an application environment that doesn't already include xpath. I assert that a large (and growing) set of language environments *already include* xpath so you dont have to implement them yourself. But yes if your using an environment where you dont have access to XPath then you'll have to write it yourself, and that is daunting. Similarly to say languages that have no support for String object or support for loops or arrays or javascript or <insert feature X> Or more to the point what if your language doesn't have an XML parser ? does that make reliance on XML "bad" ? This is a similar situation every 'generation' of languages/toolkits. At first new technologies are not omnipresent so you have to write them yourself. Eventually the winners become omnipresent. Summarize: I suggest your question really is about language and toolkit environments and whats included already, not about XPath itself. ---------------------------------------- David A. Lee dlee@calldei.com http://www.xmlsh.org -----Original Message----- From: Costello, Roger L. [mailto:costello@mitre.org] Sent: Saturday, May 07, 2011 11:12 AM To: xml-dev@lists.xml.org Subject: RE: Concerned about the increasing reliance on XPath Hi David, > But do you have support to your assertion that xpath requires large > computation for simple expressions ? If I write an application that will process an XML vocabulary and that can contain XPath then my application must implement the entire XPath specification. Michael Kay's book on XPath 2.0 is 552 pages [1]. That's a lot of stuff for my application to implement. Are you making a distinction when you say "xpath ... for simple expressions"? Note that, for example, the new XML Schema assert element (mostly) permits the entire XPath language. It does not restrict it to a "simple expressions" subset. /Roger [1] http://www.amazon.com/XPath-2-0-Programmers-Reference-Programmer/dp/07645691 04/ref=sr_1_3?ie=UTF8&qid=1304780709&sr=8-3 -----Original Message----- From: David Lee [mailto:dlee@calldei.com] Sent: Saturday, May 07, 2011 10:59 AM To: Costello, Roger L.; xml-dev@lists.xml.org Subject: RE: Concerned about the increasing reliance on XPath Contra-point. Do you have any tangible evidence that using XPath with simple expressions requires significant processing ? Its true that it requires the support infrastructure - and the same can be said of any level of computation that requires a lower layer (which is prety much all ). But do you have support to your assentation that xpath requires large computation for simple expressions ? ---------------------------------------- David A. Lee dlee@calldei.com http://www.xmlsh.org -----Original Message----- From: Costello, Roger L. [mailto:costello@mitre.org] Sent: Saturday, May 07, 2011 9:52 AM To: xml-dev@lists.xml.org Subject: Concerned about the increasing reliance on XPath Hi Folks, XPath is a fabulous language. It is incredibly powerful. It is a large, rich language. I have observed in increasing usage of XPath. For example, in XML Schema 1.1 the new assert element uses XPath to express constraints: <assert test="XPath" /> XPath gives a lot of power to the assert element. But it also means that a lot of power is needed to evaluate the assert element. To evaluate that tiny, innocuous assert element you need to implement the entire XPath language. Suppose the assert element was simplified. The only kind of assertion that can be made is, "The value of the first child element must be greater than the value of the second child element." Here's how we might use it to express the constraint between a meeting's start time and end time: <greaterThan> <element name="start-time" type="dateTime" /> <element name="end-time" type="dateTime" /> </greaterThan> Very little power is needed to evaluate this "assertion". The assertion is expressed entirely in XML markup. We've lost an enormous amount of power/expressivity. But we've gained in reduced cost of evaluation/processing/coding. While XPath is nice, it is: - not XML - requires huge amounts of processing (i.e., coding) wherever it's used I am concerned about the increasing reliance on XPath. My Position: In some cases it would be better to ratchet down capabilities and use XML markup rather than XPath. I know many people will disagree with my position. Let's have a good discussion of the issue. Here's the issue: Issue: Is the increasing reliance on XPath a positive or negative trend? (Implicit in this "issue" is an assumption that there is indeed a growing trend toward using XPath) /Roger _______________________________________________________________________ XML-DEV is a publicly archived, unmoderated list hosted by OASIS to support XML implementation and development. To minimize spam in the archives, you must subscribe before posting. [Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/ Or unsubscribe: xml-dev-unsubscribe@lists.xml.org subscribe: xml-dev-subscribe@lists.xml.org List archive: http://lists.xml.org/archives/xml-dev/ List Guidelines: http://www.oasis-open.org/maillists/guidelines.php _______________________________________________________________________ XML-DEV is a publicly archived, unmoderated list hosted by OASIS to support XML implementation and development. To minimize spam in the archives, you must subscribe before posting. 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