对GML中时态信息的分析
在GML3中已经可以表达时态信息。GML3中的时间模式对GML的核心元素进行了扩展，使其包括了可以对地理数据的时间特征进行描述的元素。其目的是描述和定义构成一门语言的结构，即提供一种用来描述一个动态的、基于要素的时间模式的历史的方法，用XML模式或一个要素集合的生命周期来表达这些结构。基本的时空模型致力与调节要素层和属性层的时间戳，并且支持对移动目标的跟踪。
时态模式由temporal.xsd，temporalComplexes.xsd两个模式文档组成，它们通过<include>元素引人了复合单位模式units.xsd中的定义和声明。
GML时态模式包括描述几何和拓扑、时态参考系统和地理数据时态特征的组件。表示的模型构成了概念模式的专用标准。基本的时空模型致力于提供要素层（feature-level）和属性层（attribute-level）的时间戳（time stamping），并且支持跟踪移动目标。
度量时间（Time）有两种类型的尺度：间隔和次序。间隔尺度为测量时间的持续性提供了基础；次序尺度提供了时间的相对位置信息（例如，一个地层次序或地质时间尺度）。
其它两个与描述时态对象有关的ISO标准是：ISO 8601，将时刻（time instants）和时段（time periods）描述成具有特殊结构和标点的文本串的编码。ISO 11404，详细描述了时距（time intervals），作为一种独立于语言的数据类型的一般讨论的一部分。
时态模式由两个相关的主题组成：三个模式文档提供了表示时刻、时段、时态拓扑和参考系统的基本元素；一个更为专门化的用于表示动态要素的模式文档组件。下图是GML中时态模式的层次结构。
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