9> erlsom:simple_form(Xml).
{ok,{"shopping",[],[{"item",[{"price","2.50"},{"quantity","3"},{"name","bread"}],[]},{"item",[{"price","3.50"},{"quantity","2"},{"name","milk"}],[]}]}," "}
10>

首先设计XML的XSD,然后使用XSD打通数据模型使用的各个环节,比如生成C#代码,直接获得强类型的对象,这个方法在.net里面很常用;erlsom提供的Data binder的模式,其实就是实现了这种设计方法;起点还是设计XSD文件,好吧,我们为上面的test2.xml设计一个XSD,如下:

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"><xsd:element name="shopping" type="shoppingType"/>
<xsd:complexType  name="shoppingType"><xsd:sequence><xsd:element name="item" minOccurs="0" maxOccurs="unbounded"><xsd:complexType><xsd:attribute name="name" type="xsd:string" use="required"/><xsd:attribute name="quantity" type="xsd:positiveInteger" use="required"/><xsd:attribute name="price" type="xsd:decimal" use="required"/></xsd:complexType></xsd:element></xsd:sequence></xsd:complexType >
</xsd:schema>

然后我们通过XSD生成对应的record,这个erlsom已经提供了工具:

 28> erlsom:write_xsd_hrl_file("test.xsd","test.hrl").
ok

打开test.hrl,对应的record已经生成:

%% HRL file generated by ERLSOM
%%
%% It is possible to change the name of the record fields.
%%
%% It is possible to add default values, but be aware that these will
%% only be used when *writing* an xml document.-record('shoppingType', {anyAttribs, 'item'}).
-record('shoppingType/item', {anyAttribs, 'name', 'quantity', 'price'}).

为了能在Erlang Shell中完成所有的测试,后面需要使用record的时候我们使用rd()命令,在shell中建立record的定义.

下面就是解析并映射为record了:

Eshell V5.9.1  (abort with ^G)
1>  {ok, X} = erlsom:compile_xsd_file("test.xsd").=ERROR REPORT==== 20-Jul-2012::06:53:09 ===
Call to tuple fun {erlsom_parse,xml2StructCallback}.Tuple funs are deprecated and will be removed in R16. Use "fun M:F/A" instead, f
or example "fun erlsom_parse:xml2StructCallback/2".(This warning will only be shown the first time a tuple fun is called.){ok,{model,[{type,'_document',sequence,[{el,[{alt,shopping,shoppingType,[],1,1,true,undefined}],1,1,1}],[],undefined,undefined,1,1,1,false,undefined},{type,shoppingType,sequence,[{el,[{alt,item,'shoppingType/item',[],1,1,true,undefined}],0,unbound,1}],[],undefined,undefined,2,1,1,undefined,undefined},{type,'shoppingType/item',sequence,[],[{att,name,1,false,char},{att,quantity,2,false,char},{att,price,3,false,char}],undefined,undefined,4,1,1,undefined,undefined}],[{ns,"http://www.w3.org/2001/XMLSchema","xsd"}],undefined,[]}}
2> {ok, Xml} = file:read_file("test2.xml").
{ok,<<"锘??xml version=\"1.0\"?>\r\n<shopping> \r\n  <item name=\"bread\" quanti
ty=\"3\" price=\"2.50\"/> \r\n  <item name=\"milk"...>>}
3> {ok, Result, _} = erlsom:scan(Xml, X).
{ok,{shoppingType,[],[{'shoppingType/item',[],"bread","3","2.50"},{'shoppingType/item',[],"milk","2","3.50"}]}," "}
4>

对于不太复杂的XML,解析到这种程度实际上已经非常方便处理了,完全可以在此停住完成最终运算;但是对于特别复杂的XML使用Record处理,更灵活直观,我们把这个流程走完:

5> rd('shoppingType', {anyAttribs, 'item'}).
shoppingType
6> rd('shoppingType/item', {anyAttribs, 'name', 'quantity', 'price'}).
'shoppingType/item'
7> R4#shoppingType.'item'.
[#'shoppingType/item'{anyAttribs = [],name = "bread",quantity = "3",price = "2.50"},
#'shoppingType/item'{anyAttribs = [],name = "milk",quantity = "2",price = "3.50"}]8> hd(R4#shoppingType.'item').
#'shoppingType/item'{anyAttribs = [],name = "bread",quantity = "3",price = "2.50"}
9> #'shoppingType/item'.quantity.
4

其它可选方案

[1] JSON 作为轻量级的数据交换格式,JSON有着巨大的优势,erlang相关解决方案也有很多比如ejson mochiweb也有相关模块

[2] Google的Protocol Buffers 以及Facebook的Thrift为代表的解决方法

[3] Piqi includes a data serialization system for Erlang. It can be used for serializing Erlang values in 4 different formats: Google Protocol Buffers, JSON, XML and Piq. http://piqi.org/#usecasesandlimitations

[4]ASN.1      ASN.1本身只定义了表示信息的抽象句法，但是没有限定其编码的方法。各种ASN.1编码规则提供了由ASN.1描述其抽象句法的数据的值的传送语法（具体表达）。标准的ASN.1编码规则有基本编码规则（BER，Basic Encoding Rules）、规范编码规则（CER，Canonical Encoding Rules）、唯一编码规则（DER，Distinguished Encoding Rules）、压缩编码规则（PER，Packed Encoding Rules）和XML编码规则（XER，XML Encoding Rules）。为了使ASN.1能够描述一些原先没有使用ASN.1定义，因此不适用上述任一编码规则的数据传输和表示的应用和协议，另外制订了ECN来扩展ASN.1的编码形式。ECN可以提供非常灵活的表明方法，但还没有得到普遍应用。

ASN.1与特定的ASN.1编码规则一起通过使用独立于计算机架构和编程语言的方法来描述数据结构，为结构化数据的交互提供了手段，特别是在网络环境的应用程序。

Erlang对ASN.1支持:

The Asn1 application provides:
• An ASN.1 compiler for Erlang, which generates encode and decode functions to be used by Erlang programs
sending and receiving ASN.1 specified data.
• Run-time functions used by the generated code.
• The supported encoding rules are:
• Basic Encoding Rules (BER)
• Distinguished Encoding Rules (DER), a specialized form of BER that is used in security-conscious
applications.
• Packed Encoding Rules (PER) both the aligned and unaligned variant.

相关:

[墙内] Processing XML in Erlang http://www.cnblogs.com/me-sa/articles/2673940.html
record to xml http://www.cnblogs.com/me-sa/articles/2673945.html

http://userprimary.net/posts/2011/02/16/Generating-XML-in-Erlang-Using-xmerl/

http://www.erlang.org/doc/apps/xmerl/xmerl_xs_examples.html
http://www.sics.se/~joe/ericsson/xml/xml.html
http://sourceforge.net/scm/?type=cvs&group_id=157642
http://stackoverflow.com/questions/3517914/erlang-xml-to-tuples-and-lists