SXML Package
SXML Package
============
SXML package contains a collection of tools for processing markup documents
(XML, XHTML, HTML) in the form of S-expressions (SXML, SHTML)
You can find the API documentation in:
http://modis.ispras.ru/Lizorkin/Apidoc/index.html
SXML tools tutorial (under construction):
http://modis.ispras.ru/Lizorkin/sxml-tutorial.html
==========================================================================
Description of the main high-level package components
-----------------------------------------------------
1. SXML-tools
2. SXPath - SXML Query Language
3. SXPath with context
4. DDO SXPath
5. Functional-style modification tool for SXML
6. XPathLink - query language for a set of linked documents
-------------------------------------------------
1. SXML-tools
XML is XML Infoset represented as native Scheme data - S-expressions.
Any Scheme programm can manipulate SXML data directly, and DOM-like API is not
necessary for SXML/Scheme applications.
SXML-tools (former DOMS) is just a set of handy functions which may be
convenient for some popular operations on SXML data.
library file: Bigloo, Chicken, Gambit: "sxml/sxml-tools.scm"
PLT: "sxml-tools.ss"
http://www.pair.com/lisovsky/xml/sxmltools/
-------------------------------------------------
2. SXPath - SXML Query Language
SXPath is a query language for SXML. It treats a location path as a composite
query over an XPath tree or its branch. A single step is a combination of a
projection, selection or a transitive closure. Multiple steps are combined via
join and union operations.
Lower-level SXPath consists of a set of predicates, filters, selectors and
combinators, and higher-level abbreviated SXPath functions which are
implemented in terms of lower-level functions.
Higher level SXPath functions are dealing with XPath expressions which may be
represented as a list of steps in the location path ("native" SXPath):
(sxpath '(table (tr 3) td @ align))
or as a textual representation of XPath expressions which is compatible with
W3C XPath recommendation ("textual" SXPath):
(sxpath "table/tr[3]/td/@align")
An arbitrary converter implemented as a Scheme function may be used as a step
in location path of "native" SXPath, which makes it extremely powerful and
flexible tool. On other hand, a lot of W3C Recommendations such as XSLT,
XPointer, XLink depends on a textual XPath expressions.
It is possible to combine "native" and "textual" location paths and location
step functions in one query, constructing an arbitrary XML query far beyond
capabilities of XPath. For example, the query
(sxpath `("document/chapter[3]" ,relevant-links @ author)
makes a use of location step function relevant-links which implements an
arbitrary algorithm in Scheme.
SXPath may be considered as a compiler from abbreviated XPath (extended with
native SXPath and location step functions) to SXPath primitives.
library file: Bigloo, Chicken, Gambit: "sxml/sxpath.scm"
PLT: "sxpath.ss"
http://www.pair.com/lisovsky/query/sxpath/
-------------------------------------------------
3. SXPath with context
SXPath with context provides the effective implementation for XPath reverse
axes ("parent::", "ancestor::" and such) on SXML documents.
The limitation of SXML is the absense of an upward link from a child to its
parent, which makes the straightforward evaluation of XPath reverse axes
ineffective. The previous approach for evaluating reverse axes in SXPath was
searching for a parent from the root of the SXML tree.
SXPath with context provides the fast reverse axes, which is achieved by
storing previously visited ancestors of the context node in the context.
With a special static analysis of an XPath expression, only the minimal
required number of ancestors is stored in the context on each location step.
library file: Bigloo, Chicken, Gambit: "sxml/xpath-context.scm"
PLT: "xpath-context_xlink.ss"
-------------------------------------------------
4. DDO SXPath
The optimized SXPath that implements distinct document order (DDO) of the
nodeset produced.
Unlike conventional SXPath and SXPath with context, DDO SXPath guarantees that
the execution time is at worst polynomial of the XPath expression size and of
the SXML document size.
The API of DDO SXPath is compatible of that in conventional SXPath. The main
following kinds of optimization methods are designed and implemented in DDO
SXPath:
- All XPath axes are implemented to keep a nodeset in distinct document
order (DDO). An axis can now be considered as a converter:
nodeset_in_DDO --> nodeset_in_DDO
- Type inference for XPath expressions allows determining whether a
predicate involves context-position implicitly;
- Faster evaluation for particular kinds of XPath predicates that involve
context-position, like: [position() > number] or [number];
- Sort-merge join algorithm implemented for XPath EqualityComparison of
two nodesets;
- Deeply nested XPath predicates are evaluated at the very beginning of the
evaluation phase, to guarantee that evaluation of deeply nested predicates
is performed no more than once for each combination of
(context-node, context-position, context-size)
library file: Bigloo, Chicken, Gambit: "sxml/ddo-txpath.scm"
PLT: "ddo-txpath.ss"
http://modis.ispras.ru/Lizorkin/ddo.html
-------------------------------------------------
5. Functional-style modification tool for SXML
A tool for making functional-style modifications to SXML documents
The basics of modification language design was inspired by Patrick Lehti and
his data manipulation processor for XML Query Language:
http://www.ipsi.fraunhofer.de/~lehti/
However, with functional techniques we can do this better...
library file: Bigloo, Chicken, Gambit: "sxml/modif.scm"
PLT: "modif.ss"
-------------------------------------------------
6. XPathLink - query language for a set of linked documents
XLink is a language for describing links between resources using XML attributes
and namespaces. XLink provides expressive means for linking information in
different XML documents. With XLink, practical XML application data can be
expressed as several linked XML documents, rather than a single complicated XML
document. Such a design makes it very attractive to have a query language that
would inherently recognize XLink links and provide a natural navigation
mechanism over them.
Such a query language has been designed and implemented in Scheme. This
language is an extension to XPath with 3 additional axes. The implementation
is naturally an extended SXPath. We call this language XPath with XLink
support, or XPathLink.
Additionally, an HTML <A> hyperlink can be considered as a particular case of
an XLink link. This observation makes it possible to query HTML documents with
XPathLink as well. Neil W. Van Dyke <[email protected]> and his permissive
HTML parser HtmlPrag have made this feature possible.
library file: Bigloo, Chicken, Gambit: "sxml/xlink.scm"
PLT: "xpath-context_xlink.ss"
http://modis.ispras.ru/Lizorkin/xpathlink.html
==========================================================================
Examples and expected results
-----------------------------
Obtaining an SXML document from XML
(sxml:document "http://modis.ispras.ru/Lizorkin/XML/poem.xml")
==>
(*TOP*
(*PI* xml "version='1.0'")
(poem
(@ (title "The Lovesong of J. Alfred Prufrock") (poet "T. S. Eliot"))
(stanza
(line "Let us go then, you and I,")
(line "When the evening is spread out against the sky")
(line "Like a patient etherized upon a table:"))
(stanza
(line "In the room the women come and go")
(line "Talking of Michaelangelo."))))
Accessing parts of the document with SXPath
((sxpath "poem/stanza[2]/line/text()")
(sxml:document "http://modis.ispras.ru/Lizorkin/XML/poem.xml"))
==>
("In the room the women come and go" "Talking of Michaelangelo.")
Obtaining/querying HTML documents
((sxpath "html/head/title")
(sxml:document "http://modis.ispras.ru/Lizorkin/index.html"))
==>
((title "Dmitry Lizorkin homepage"))
-------------------------------------
SXML Transformations
Pre-post-order transformations (requires SSAX package)
(pre-post-order
(sxml:document "http://modis.ispras.ru/Lizorkin/XML/poem.xml")
`((*TOP* *macro* . ,(lambda top (car ((sxpath '(*)) top))))
(poem
unquote
(lambda elem
`(html
(head
(title ,((sxpath "string(@title)") elem)))
(body
(h1 ,((sxpath "string(@title)") elem))
,@((sxpath "node()") elem)
(i ,((sxpath "string(@poet)") elem))))))
(@ *preorder* . ,(lambda x x))
(stanza . ,(lambda (tag . content)
`(p ,@(map-union (lambda (x) x) content))))
(line . ,(lambda (tag . content) (append content '((br)))))
(*text* . ,(lambda (tag text) text))))
==>
(html
(head (title "The Lovesong of J. Alfred Prufrock"))
(body
(h1 "The Lovesong of J. Alfred Prufrock")
(p
"Let us go then, you and I,"
(br)
"When the evening is spread out against the sky"
(br)
"Like a patient etherized upon a table:"
(br))
(p "In the room the women come and go" (br)
"Talking of Michaelangelo." (br))
(i "T. S. Eliot")))
-------------------------------------
XPathLink: a query language with XLink support
Returning a chapter element that is linked with the first item
in the table of contents
((sxpath/c "doc/item[1]/traverse::chapter")
(xlink:documents "http://modis.ispras.ru/Lizorkin/XML/doc.xml"))
==>
((chapter (@ (id "chap1"))
(title "Abstract")
(p "This document describes about XLink Engine...")))
Traversing between documents with XPathLink
((sxpath/c "descendant::a[.='XPathLink']/traverse::html/
descendant::blockquote[1]/node()")
(xlink:documents "http://modis.ispras.ru/Lizorkin/index.html"))
==>
((b "Abstract: ")
"\r\n"
"XPathLink is a query language for XML documents linked with XLink links.\r\n"
"XPathLink is based on XPath and extends it with transparent XLink support.\r\n"
"The implementation of XPathLink in Scheme is provided.\r\n")
-------------------------------------
SXML Modifications
Modifying the SXML representation of the document
((sxml:modify '("/poem/stanza[2]" move-preceding "preceding-sibling::stanza"))
(sxml:document "http://modis.ispras.ru/Lizorkin/XML/poem.xml"))
==>
(*TOP*
(*PI* xml "version='1.0'")
(poem
(@ (title "The Lovesong of J. Alfred Prufrock") (poet "T. S. Eliot"))
(stanza
(line "In the room the women come and go")
(line "Talking of Michaelangelo."))
(stanza
(line "Let us go then, you and I,")
(line "When the evening is spread out against the sky")
(line "Like a patient etherized upon a table:"))))
-------------------------------------
DDO SXPath: the optimized XPath implementation
Return all text nodes that follow the keyword ``XPointer'' and
that are not descendants of the element appendix
((ddo:sxpath "//text()[contains(., 'XPointer')]/
following::text()[not(./ancestor::appendix)]")
(sxml:document "http://modis.ispras.ru/Lizorkin/XML/doc.xml"))
==>
("XPointer is the fragment identifier of documents having the mime-type..."
"Models for using XLink/XPointer "
"There are important keywords."
"samples"
"Conclusion"
"Thanks a lot.")
-------------------------------------
Lazy XML processing
Lazy XML-to-SXML conversion
(define doc
(lazy:xml->sxml
(open-input-resource "http://modis.ispras.ru/Lizorkin/XML/poem.xml")
'()))
doc
==>
(*TOP*
(*PI* xml "version='1.0'")
(poem
(@ (title "The Lovesong of J. Alfred Prufrock") (poet "T. S. Eliot"))
(stanza (line "Let us go then, you and I,") #<struct:promise>)
#<struct:promise>))
Querying a lazy SXML document, lazyly
(define res ((lazy:sxpath "poem/stanza/line[1]") doc))
res
==>
((line "Let us go then, you and I,") #<struct:promise>)
Obtain the next portion of the result
(force (cadr res))
==>
((line "In the room the women come and go") #<struct:promise>)
Converting the lazy result to a conventional SXML nodeset
(lazy:result->list res)
==>
((line "Let us go then, you and I,")
(line "In the room the women come and go"))
![[logo]](/logo.png){kind=logo}