In the world of traditional Geographic Information Systems people usually make a distinction between graphics data (which consists of polygons, arcs, points, displayed text, etc.) and attribute data (which consists of textual descriptions of the information). A typical GIS generally views spatial data as graphics with associated attributes. A polygon has attributes such as species1, species2, etc. With SAIF the separation between graphics and non-graphics is de-emphasized. SAIF introduces higher level structures which contain an arbitrary number of attributes; some of these attributes may describe space, time and topology, and still others traditional attributes. The italicized sentence above becomes the following. A forest stand has several attributes, including species1, species2, and a position in space represented as a polygon. Thus the term attribute is used regardless of the nature of the attribution.
With SAIF, the information is considered as a series of objects, each of which comes from a given type or class. South Moresby Island in British Columbia is an object representing an instance (i.e. an example) of the general notion of Park. The fact that South Moresby Island is an example of a park and not a resort or a restaurant is an inherent part of the data. We know it is a park without having to decipher it from the attributes and attribute values used to describe it. Thus the notion of an object is that of something which is directly meaningful to us: it is not necessary to look inside of it to decide what it is. The way we are likely to think about an object and the way it is characterized formally are semantically equivalent.
class: an abstract data type which describes a group of objects that share the same characteristics. A class defines a unique collection of attributes and methods which distinguish it from all other classes. A class does not store any data; it is merely a template from which objects are created.
object: a unit of data which may be treated as indivisible at a higher level of abstraction. It is an instance, i.e., a value, of a class. An object may have an explicitly provided object identifier.
geographic object: an object representing a real world phenomenon which exists in a spatial or spatiotemporal domain. An object is considered a geographic object if its position in space, or in both space and time, forms an integral part of our understanding of the object.
spatial object: Consider a given geographic object defined as occupying a region in space. That region is represented by a spatial object. There are two aspects to a spatial object: geometry and spatial referencing. The geometry defines the object's shape and is expressed in terms of point, line, area and volume concepts. Coordinate values are provided as part of the geometry. The interpretation of the coordinates depends on the definition of the space in which they reside. Spatial referencing provides that definition by stating the coordinate system and the horizontal and vertical reference systems.
spatiotemporal object: Next consider a given geographic object defined as occupying a region in both space and time. That region is represented by a spatiotemporal object. There are four aspects to a spatiotemporal domain: geometry, spatial referencing, time, and temporal referencing. Geometry and spatial referencing are as described above. Time values may indicate relative or absolute times or dates, as well as durations. Temporal referencing states whether the time values are based on Universal Coordinated Time (UTC), whether GPS timing applies, and the offset in hours and minutes from UTC.
annotation An annotation object is comprised entirely of text and/or symbols which may be spatially referenced. (Toponymy and swamp symbols are typical examples.)
South Moresby Island is a geographic object belonging to the class Park. More precisely we can say that it is a real world phenomenon represented as an object belonging to the class Park. The object may also be considered as a member of the class Island; that is, it may be an instance of several classes. The words Pacific Ocean on a map of the area comprise an annotation object.