A property is the atomic data element that is used store data of a specific type within a property structure. Each property is of a specific property type which defines what kind of data (numeric, text, Boolean, etc).can be stored with that property. Besides properties a property structure can also contain collections of other property structures. This way property collections can be used to form one to many relationships with a property structure, i..e. if one instance of a property structure shall contain a series of elements with the same characteristics where the number of those elements can vary.

Example: A property structure used to store type specific data for observations that describe the geological situation at a specific location this description may include any number of rock types observed at this location. In one case you might have just one rock type in other cases you may have five or more. To cleanly represent this, collections would be used.

A property structure containing property collections is called a hierarchical property structure, a property structure containing no collections is called a flat property structure. Since the members of a property collections are also property structures property structures can be nested in any depth

A flat property structure has depth 0, a property structure containing collections which contain only properties has depth 1, a property structure with collections that contain other collections has depth 2 and so on. The level of a property within a property is the collection level in which it was defined. Properties defined directly on the property structure and in no collection are on level 0.

Figure 1 shows a flat property structure, Figure 2 shows a hierarchical property structure. In figure 1 the depth of the property structure is zero, and all properties are on level zero, in figure 2 the depth of the property structure is 2 the property Property Aa1 is on level 2.