1、XMerL,Interfacing XML and ErlangUlf Wiger, Senior Systems Architect Network Architecture and Product Strategies Data Backbone and Optical Networks Division Ericsson Telecom AB,Executive Summary,Erlang/OTP is moving into vertical applications XML is fast becoming an important standard Erlang and XML
2、fit very well together,Number of Requests to www.erlang.org,The Reason for XMerL,Interest in Erlang is growing No longer just for embedded systems New interfaces must evolve Powerful GUI components Data exchange (COM, ODBC, XML, ) XML is a logical addition to OTP (ASN.1, HTTP, IDL, CORBA, )Real reas
3、on: I bought a book and became curious,What is XML?,“A Stricter HTML” “A Simpler SGML” Relatively Easy to Parse Content OrientedXML springs mostly from SGML All non-essential SGML features have been removed Web address support taken from HTML, HyTime and TEI Some new functionality added Modularity E
4、xtensibility through powerful linking International (Unicode) support Data orientation,Where is XML used?,Large Web sites HTML is generated via special (XSL) stylesheets Internet Explorer has built-in support for XML Document management When machines must be able to read the documents Machine-to-mac
5、hine communication XML RPC, SOAP XML processors exist in many languages (even Erlang!),A Simple XML Document,Welcome to My Home PageSorry, this home page is still under construction. Please come back soon!,All elements must have a start tag and an end tag (exception: ) An element can have a list of
6、attributes,Erlang analogy: Tag, Attributes, Content,A Simple Erlang-XML Document,Welcome to My Home PageSorry, this home page is still under construction. Please come back soon!,XML,Almost equivalent,The Complete Picture,XML is more complex than that External DTDs Global namespace Language encoding
7、Structural information should be optimized for queries To parse XML properly, we use records To output to XML (or similar), we may use the simple form,XMerL Status,A fast XML processor produces an Erlang representation of the XML document Lets call this representation a “complete form” Erlang progra
8、ms can use an XML-like representation Lets call this a “simple form” An export tool can take either form and output almost anything Plans to support XML Stylesheets (XSL, more on that later) Basic support for XPATH (needed for XSL, Xlink, Xpointer, ),The XMerL Processor,Vsn 0.6 is a single-pass scan
9、ner/parser implementing XML 1.0 Has been tested on thousands of XML documents Appears to handle lots of different documents Appears to be fast and flexible There are two ways to process an XML document: Tree-based parsing; the whole document at once Event-based parsing; one element at a time The XMe
10、rL processor can do either The behaviour is specified through higher-order functions (“funs”) Validation can also be carried out in funs,The XMerL Processor (2),Proper handling of Global namespace Entity expansion External and internal DTDs Conditional processing UniCode Some support for infinite st
11、reams,The XMerL Export Tool,The export tool takes a complete or simple form and outputs some (almost arbitrary) data structure Translation takes place in callback modules: CBModule:Tag(Content, Attributes, Parents, CompleteRecord) A callback module can inherit other callback modules A callback funct
12、ion can do three things: Return data on some output format Point to another callback function (alias) Return a modified (simple or complete) form for re-processing Existing callback modules HTML (not yet complete) XML (generic, not complete),Simple Export Tool Example,foo() -xmerl:export_simple(simp
13、le(), xmerl_html, title, “Doc Title“).foo2() -xmerl:export_simple(simple(), xmerl_xml, title, “Doc Title“).simple() -document, title, “Doc Title“, author, “Ulf Wiger,section, heading, “heading1“,P, “This is a paragraph of text.“,section, heading, “heading2“,P, “This is another paragraph.“,table, bor
14、der, 1, heading, col, “head1“,col, “head2“,row, col, “col11“,col, “col12“,row,col, “col21“,col, “col22“.,Export to HTML,foo() -xmerl:export_simple(simple(), xmerl_html, title, “Doc Title“).foo2() -xmerl:export_simple(simple(), xmerl_xml, title, “Doc Title“).simple() -document, title, “Doc Title“, au
15、thor, “Ulf Wiger,section, heading, “heading1“,P, “This is a paragraph of text.“,section, heading, “heading2“,P, “This is another paragraph.“,table, border, 1, heading, col, “head1“,col, “head2“,row, col, “col11“,col, “col12“,row,col, “col21“,col, “col22“.,Sample Code:% section/3 is to be used instea
16、d of headings. section(Data, Attrs, section,_, section,_, section,_ | _, E) -opt_heading(Attrs, “, “, Data); section(Data, Attrs, section,_, section,_ | _, E) -opt_heading(Attrs, “, “, Data); section(Data, Attrs, section,_ | _, E) -opt_heading(Attrs, “, “, Data); section(Data, Attrs, Parents, E) -op
17、t_heading(Attrs, “, “, Data).opt_heading(Attrs, StartTag, EndTag, Data) -case find_attribute(heading, Attrs) ofvalue, Text -StartTag, Text, EndTag, “n“ | Data;false -Dataend.,Export to XML,foo() -xmerl:export_simple(simple(), xmerl_html, title, “Doc Title“).foo2() -xmerl:export_simple(simple(), xmer
18、l_xml, title, “Doc Title“).simple() -document, title, “Doc Title“, author, “Ulf Wiger,section, heading, “heading1“,P, “This is a paragraph of text.“,section, heading, “heading2“,P, “This is another paragraph.“,table, border, 1, heading, col, “head1“,col, “head2“,row, col, “col11“,col, “col12“,row,co
19、l, “col21“,col, “col22“.,This is a paragraph of text.This is another paragraph.head1head2col11col12col21col22,Sample Code:% The #root# tag is called when the entire structure has been exported. % It does not appear in the structure itself. #root#(Data, Attrs, , E) -“n“, Data.#element#(Tag, , Attrs,
20、Parents, E) -TagStr = mk_string(Tag),“n“; #element#(Tag, Data, Attrs, Parents, E) -TagStr = mk_string(Tag),“n“, Data, opt_newline(Data),“n“.,XML Stylesheets,Stylesheet support is clearly needed Interpreting XML stylesheets is slow and cumbersome (lots of independent, heavy XPATH queries) Possible ap
21、proach: Read the stylesheets using the XMerL processor Translate them into an Erlang program Optimization opportunity: convert xsl:match statements into match criteria for a single scan function Lots more work is needed here.,More Examples.,Current xmerl version, 0.6, is on Open Source Thanks to the beta testers: Mickael Remond Luc Taesch,
