SFDU General Information

The SFDU acronym stands for Standard Formatted Data Unit. An alternative meaning is Standards For Data Understanding. SFDU is a set of international standards for packaging, classifying, and aggregating data into self-identifying data products. A standard 20-byte label begins the entire data product. More similar labels are attached to data products nested within each original data product. The SFDU standard has been extended to provide data description languages, a data dictionary structure, and Control Authority services.

SFDUs were originally proposed by Panel 2 of the CCSDS to solve the problem of data transfer between heterogeneous environments. The CCSDS is an international organization made up of representatives of most of the world's space agencies. Its Panel 2 is developing standards for the interchange and archiving of data collected in space experiments. This organization was founded because space scientists around the world realized that without a standardized way to label and package space data, it would become unmanageable to archive and retrieve huge amounts of data in many varieties of data formats. Data sent from one site to another site might be unreadable or unusable at the second site. The plan is to have software tools and services available to space scientists and agencies around the world. This would enable any user anywhere to unpack, read, and process any space data. There is the additional intention that these labels be planned in such a way that software may be written to examine the whole of an SFDU object, find certain parts of it, and automatically provide services upon or regarding the information in those certain parts. This embodies what is often referred to as the requirement that SFDUs shall be "human-readable and machine- parsible"; in other words, the labels will not be of such size or complexity as to significantly complicate a scanning by eye of the SFDU's contents, but the labels will also contain enough information so that software can usefully dissect the SFDU object.

The SFDU standard includes the description of the activities of specialized personnel whose work can be broadly characterized as combining that of librarians, advisors, and administrators. These are the personnel who staff what are called Control Authority Offices (CAOs). Another term often used for such an office is Member Agency Control Authority Office (MACAO). The functions of these offices are:

The standards that are being developed are worked on in the form of a series of "books." The development of a particular book is delegated at first to a small group of professionals involved with SFDUs. Eventually, as the book is developed, these professionals put the book out for commentary and approval by the wider community. This process is associated with the book moving through a series of stages that have been named with the colors White, Red, and Blue. White books are under review by the initial technical panel. Red books have graduated to formal review by the member agencies. Red books, while recognizably more mature than white books, are still subject to iterations and revisions. Blue books are the final result of the development. Blue books are documents that have been approved by all member agencies.

At this writing (March, 1992), the standards have all reached the "Red Book" stage, except for an explanation of fundamental SFDU structure and construction rules, which is a Blue Book. Red books are being developed on additional structure and construction rules, Control Authority Office Policies and Procedures, and technical issues concerning the computer-parsed aspects of SFDU information.


The primary focus of SFDUs is transfer of information or knowledge as opposed to the rapid access to the information. To do that, there is heavy focus on the metadata or documentation that needs to go along with the data set to make it generally usable and understandable by the science data recipients.

The SFDU is really comprised of a set of international standards and their supporting infrastructure.

In the standards area, there are a number of categories of standards. There are packaging and unpackaging standards, which include the classifications of data. There are the description languages, which are used to write documentation that describes the data. There is a dictionary structure, which is used to document or establish a standard interchange form for dictionaries. Additionally there are other services that are provided by this international organization infrastructure. These are called Control Authorities.

The Control Authorities provide an international registration process for metadata i.e. documentation about data. There are a number of coordinated services that result from the fact that they follow standards in this area.

The main function of the Control Authorities is to register descriptions and to disseminate those descriptions upon request. The way the desired data description is identified in these requests is through a particular identifier for the data. Depending on your local Control Authority, other services could include the distribution of software and the checking the metadata for completeness.

SFDU General Information Page / sfdu@nssdca.gsfc.nasa.gov

A service of NOST at NSSDC.

Author: John Garrett (John.Garrett\@gsfc.nasa.gov) +1.301.286.3575
Curator: John Garrett (John.Garrett\@gsfc.nasa.gov) +1.301.286.3575
NASA Official: Don Sawyer (Donald.M.Sawyer@nasa.gov) +1.301.286.2748
Last Revised: March 1, 1995, John Garrett