關于什么是GUID，ProgID ，CLSID和UID，在ESRI的Document Library能夠找到下面的描述.
COM interfaces and coclasses are identified by a globally unique identifier (GUID). The GUID for an interface is called an interface ID (IID). The GUID for a coclass is called class ID (CLSID). A ProgID is a text alias for a CLSID; the ProgID is a string composed of the project name and the class name of the coclass.
The UID coclass can be used to represent the GUID of an object.
There is built-in module called ArcID in the VBA project for the Normal template in both ArcMap and ArcCatalog. This module is a utility for finding the UID of the built-in commands and toolbars. You pass the name of a command or toolbar in as an argument to ArcID and the UID of that item is returned. The ArcID module is regenerated every time the Normal template is loaded; the registry is read to get the GUIDs of all the commands and toolbars that are currently used by the application.
簡單的說，GUID(全局统一标识符)是用來標識識別COM接口和組件，保证它們的唯一性，避免出現版本不一致而導致的組件沖突.IID就是接口的GUID表示，CLSID則是組件類的GUID表示。ProgID是程序员给某个CLSID指定一个易记的名字.UID則是物象（Object)的GUID. 以下是一些ILayer接口的UID,通過使用它們，我們可以快速找到所需的圖層。 這些ESRI接口存放在注冊表中的 HKEY_CLASSES_ROOT下面，如果想查詢它們的UID，可以通過查找它們的名字，從而找到對應的UID.
下面是一個查找groupLayer的例子