The Spatial Archive and Interchange Format (SAIF, pronounced safe) was defined in the early 1990s as a self-describing, extensible format designed to support interoperability and storage of geospatial data. SAIF dataset SAIF has two major components that together define SAIFtalk. The first is the Class Syntax Notation (CSN), a data definition language used to define a dataset's schema. The second is the Object Syntax Notation (OSN), a data language used to represent the object data adhering to the schema. The CSN and OSN are contained in the same physical file, along with a directory at the beginning of the file. The use of ASCII text and a straightforward syntax for both CSN and OSN ensure that they can be parsed easily and understood directly by users and developers. A SAIF dataset, with a or extension, is compressed using the zip archive format. Schema definition SAIF defines 285 classes (including enumerations) in the Class Syntax Notation, covering the definitions of high-level features, geometric types, topological relationships, temporal coordinates and relationships, geodetic coordinate system components and metadata. These can be considered as forming a base schema. Using CSN, a user defines a new schema to describe the features in a given dataset. The classes belonging to the new schema are defined in CSN as subclasses of existing SAIF classes or as new enumerations. A ForestStand::MySchema for example could be defined with attributes including age, species, etc. and with ForestStand::MySchema specified as a subclass of GeographicObject, a feature defined in the SAIF standard. All user defined classes must belong to a schema, one defined by the user or previously existing. Different schemas can exist in the same dataset and objects defined under one schema can reference those specified in another. Inheritance SAIF supports multiple inheritance, although common usage involved single inheritance only. Object referencing Object referencing can be used as a means of breaking up large monolithic structures. More significantly, it can allow objects to be defined only once and then referenced any number of times. A section of the geometry of the land-water interface could define part of a coastline as well as part of a municipal boundary and part of a marine park boundary. This geometric feature can be defined and given an object reference, which is then used when the geometry of the coastline, municipality and marine park are specified. Multimedia Multimedia objects can also be objects in a SAIF