[Web开发] 微软的RSS协议扩展 - FeedSync 介绍 (2)

下面通过一个例子来解释 FeedSync 协议。 该例子讲述当没有数据一致性冲突发生的的时候，FeedSync 如何工作。

这是一个简单基于RSS协议的XML， 描述我今天的任务列表。

<? xml version="1.0" encoding="utf-8" ?>
< rss  version ="2.0" >
   < channel >
     < title > todolist.xml </ title >
     < description > Sample to do list </ description >
     < link > http://www.example.com/index.html </ link >
     < item >
       < title > Pay Bills </ title >
       < description > Electric, Gas and Water Bills </ description >
     </ item >
   </ channel >
</ rss >

FeedSync 扩展在<item>下面加入了<sx:sync> 标签 以及 <sx:history> 标签

<? xml version="1.0" ?>
< rss  version ="2.0"  xmlns:sx ="http://feedsync.org/2007/feedsync" >
     < channel >
         < title > todolist.xml </ title >
         < description > Sample to do list </ description >
         < link > http://www.example.com/index.html </ link >
         < item >
             < sx:sync  id ="101"  updates ="1"  deleted ="false"  noconflicts ="false" >
                 < sx:history  sequence ="1"  when ="2007-11-29T06:27:11Z"  by ="fsRSSConvert.js" />
             </ sx:sync >
             < title > Pay Bills </ title >
             < description > Electric, Gas and Water Bills </ description >
         </ item >
     </ channel >
</ rss >

假设我有2台电脑（台式机和笔记本）， 在台式电脑A 上我增加了“Buy groceries” 以及“Get car serviced” 任务项； 过了一会儿，我又在笔记本电脑B 上我增加了“Return books to library”以及“Get birthday gift for mother” 任务项。  这时，台式电脑A上的的XML 文件变成了

     < item >
       < sx:sync  id ="101"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:11Z"  by ="fsRSSConvert.js" />
       </ sx:sync >
       < title > Pay Bills </ title >
       < description > Electric, Gas and Water Bills </ description >
     </ item >
     < item >
       < sx:sync  id ="ep1.100"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:11Z"  by ="A" />
       </ sx:sync >
       < title > Buy groceries </ title >
       < description > Get milk and eggs </ description >
     </ item >
     < item >
       < sx:sync  id ="ep1.101"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:12Z"  by ="A" />
       </ sx:sync >
       < title > Get car serviced </ title >
       < description > Needs oil change </ description >
     </ item >

笔记本电脑B上的XML 文件就是

     < item >
       < sx:sync  id ="101"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:11Z"  by ="fsRSSConvert.js" />
       </ sx:sync >
       < title > Pay Bills </ title >
       < description > Electric, Gas and Water Bills </ description >
     </ item >
     < item >
       < sx:sync  id ="ep2.100"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:12Z"  by ="B" />
       </ sx:sync >
       < title > Return books to library </ title >
       < description > 2 books in total </ description >
     </ item >
     < item >
       < sx:sync  id ="ep2.101"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:12Z"  by ="B" />
       </ sx:sync >
       < title > Get birthday gift for mother </ title >
       < description > She likes blue flowers </ description >
     </ item >

当两个电脑都做数据同步之后，通过FeedSync协议，服务器上将会对两个XML进行合并，最终形成

     < item >
       < sx:sync  id ="101"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:11Z"  by ="fsRSSConvert.js" />
       </ sx:sync >
       < title > Pay Bills </ title >
       < description > Electric, Gas and Water Bills </ description >
     </ item >
     < item >
       < sx:sync  id ="ep1.100"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:11Z"  by ="A" />
       </ sx:sync >
       < title > Buy groceries </ title >
       < description > Get milk and eggs </ description >
     </ item >
     < item >
       < sx:sync  id ="ep1.101"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:12Z"  by ="A" />
       </ sx:sync >
       < title > Get car serviced </ title >
       < description > Needs oil change </ description >
     </ item >
     < item >
       < sx:sync  id ="ep2.100"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:12Z"  by ="B" />
       </ sx:sync >
       < title > Return books to library </ title >
       < description > 2 books in total </ description >
     </ item >
     < item >
       < sx:sync  id ="ep2.101"  updates ="1"  deleted ="false"  noconflicts ="false" >
         < sx:history  sequence ="1"  when ="2007-11-29T06:27:12Z"  by ="B" />
       </ sx:sync >
       < title > Get birthday gift for mother </ title >
       < description > She likes blue flowers </ description >
     </ item >