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 Geographic data and information is defined in the ISO/TC 211 series of standards as data and information having an implicit or explicit association with a location relative to Earth (a geographic location or geographic position). It is also cal ...

SAIF dataset

SAIF has two major components that together define SAIFtalk. The first is the Class Syntax Notation (CSN), a

data definition language In the context of SQL, data definition or data description language (DDL) is a syntax for creating and modifying database objects such as tables, indices, and users. DDL statements are similar to a computer programming language for defining d ...

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 Geometry (; ) is a branch of mathematics concerned with properties of space such as the distance, shape, size, and relative position of figures. Geometry is, along with arithmetic, one of the oldest branches of mathematics. A mathematician w ...

types,

topological Topology (from the Greek words , and ) is the branch of mathematics concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, wit ...

relationships, temporal coordinates and relationships,

geodetic Geodesy or geodetics is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D. It is called planetary geodesy when studying other astronomical bodies, such as planets ...

coordinate system components and

metadata Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive ...

. 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

coast A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...

line as well as part of a

municipal A municipality is usually a single administrative division having corporate status and powers of self-government or jurisdiction as granted by national and regional laws to which it is subordinate. The term ''municipality'' may also mean the gov ...

boundary and part of a

marine park A marine park is a designated park consisting of an area of sea (or lake) set aside to achieve ecological sustainability, promote marine awareness and understanding, enable marine recreational activities, and provide benefits for Indigenous peo ...

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 dataset and referenced accordingly. For example, image and sound files associated with a given location could be included.

Model transformations and related software applications

The primary advantage of SAIF was that it was inherently extensible following object oriented principles. This meant that data transfers from one GIS environment to another did not need to follow the lowest common denominator between the two systems. Instead, data could be extracted from a dataset defined by the first GIS, transformed into an intermediary, i.e., the semantically rich SAIF model, and from there transformed into a model and format applicable to the second GIS. This notion of model to model transformation was deemed to be realistic only with an

object oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of '' objects''. Objects can contain data (called fields, attributes or properties) and have actions they can perform (called procedures or methods and impleme ...

approach. It was recognized that scripts to carry out such transformations could in fact add information content. When Safe Software developed the Feature Manipulation Engine (FME), it was in large measure with the express purpose of supporting such transformations. The FMEBC was a freely available software application that supported a wide range of transformations using SAIF as the hub. The FME was developed as a commercial offering in which the intermediary could be held in memory instead of as a SAIF dataset.

History

The SAIF project was established as a means of addressing interoperability between different geographic information systems. Exchange formats of particular prominence at the time included DIGEST (Digital Geographic Information Exchange Standard) and SDTS (Spatial Data Transfer Specification, later accepted as the Spatial Data Transfer Standard). These were considered as too inflexible and difficult to use. Consequently, the

Government of British Columbia The Government of British Columbia () is the body responsible for the administration of the Canadian province of British Columbia. The term ''Government of British Columbia'' can refer to either the collective set of all three institutions, or mo ...

decided to develop SAIF and to put it forward as a national standard in

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. SAIF became a Canadian national standard in 1993 with the approval of the Canadian General Standards Board. The last version of SAIF, published in January 1995, is designated as CGIS-SAIF Canadian Geomatics Interchange Standard: Spatial Archive and Interchange Format: Formal Definition (Release 3.2), issue CAN/CGSB-171.1-95, catalogue number P29-171-001-1995E. The work on the SAIF modeling paradigm and the CSN classes was carried out principally by Mark Sondheim, Henry Kucera and Peter Friesen, all with the British Columbia government at the time. Dale Lutz and Don Murray of Safe Software developed the Object Syntax Notation and the Reader and Writer software that became part of the Feature Manipulation Engine. SAIF was brought to the attention of Michael Stonebraker and Kenn Gardels of the

University of California at Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a public land-grant research university in Berkeley, California, United States. Founded in 1868 and named after the Anglo-Irish philosopher George Berkele ...

, and then to those working on the initial version of the Open Geospatial Interoperability Specification (OGIS), the first efforts of what became the

Open Geospatial Consortium The Open Geospatial Consortium (OGC) is an international voluntary consensus standards organization that develops and maintains international standards for geospatial content and location-based services, sensor web, Internet of Things, Geographi ...

(OGC). A series of 18 submissions to the ISO SQL Multimedia working group also helped tie SAIF to the original ISO work on geospatial features. Today SAIF is of historical interest only. It is significant as a precursor to the

Geography Markup Language The Geography Markup Language (GML) is the XML grammar defined by the Open Geospatial Consortium (OGC) to express geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic ...

and as the formative element in the development of the widely used Feature Manipulation Engine.

References

* Sondheim, M., K. Gardels, and K. Buehler, 1999. GIS Interoperability. pp. 347–358. in Geographical Information Systems (Second Edition), Volume 1, edited by Paul A. Longley, Michael F. Goodchild, David J. Magurie and Davide W. Rhind. * Sondheim, M., P. Friesen, D. Lutz, and D. Murray. 1997. Spatial Archive and Interchange Format (SAIF). in Spatial Database Transfer Standards 2: Characteristics for Assessing Standards and Full Descriptions of the National and International Standards in the World. edited by Moellering H. and Hogan R. Elsevier, Netherlands. {{ISBN, 0-08-042433-3. * Surveys and Resource Mapping Branch. Spatial Archive and Interchange Format, Release 3.2, Formal Definition. 1995. (also Release 3.1 (1994); 3.0 (1993); 2.0, (1992); 1.0 (1991); and 0.1, (1990)) Surveys and Resource Mapping Branch, British Columbia Ministry of Environment, Lands and Parks. 258p. Also published by the Canadian General Standards Board, CAN/CGSB-171.1-95.

External links

Government of Canada Publications, CGIS-SAIF Release 3.2

Safe Software, 2010, FME Readers and Writers, (Spatial Archive and Interchange Format, pp. 183 - 191)
Interoperability GIS file formats Open Geospatial Consortium