/**
 * map.json
 * map的数据结构采用树型结构, 大致如下所示:
 * root
 *	|---child1
 *		|---child1-1
 *			|---child1-1-1
 *		|---child1-2
 *	|---child2
 *	|---child3
 *
 * 目前node支持如下属性:
 * node
 *	|---id
 *	|---content
 *	|---offset
 *	|---parent
 *	|---children
 *
 * map
 *	|---tree
 *	|---name
 *	|---lastModified
 */
{
	"document" : [
		{
			"id" : "child1",
			"content" : "child1",
			"offset" : {"x" : 100, "y" : 200},
			"parent" : "map",
			"children" : [
				{
					"id" : "child1-1",
					"content" : "child1-1",
					"offset" : {"x" : 100, "y" : 200},
					"parent" : "child1",
					"children" : [
						{
							"id" : "child1-1-1",
							"content" : "child1-1-1",
							"offset" : {"x" : 200, "y" : 200},
							"parent" : "child1-1",
							"children" : null
						}
					]
				},
				{
					"id" : "child1-2",
					"content" : "child1-2",
					"offset" : {"x" : 200, "y" : 200},
					"parent" : "child1",
					"children" : null
				}
			]
		},
		{
			"id" : "child2",
			"content" : "child2",
			"offset" : {"x" : 100, "y" : 100},
			"parent" : "map",
			"children" : null
		},
		{
			"id" : "child3",
			"content" : "child3",
			"offset" : {"x" : 200, "y" : 100},
			"parent" : "map",
			"children" : null
		}
	],
	"name" : "untitled",
	"lastModified" : 123456789
}