EAST(ID:8125/)for Enhanced Ada SubseT Data description language References: EAST is intended for use in a Data Descripton Record, which can be included in a CCSDS SFDU(1) as a formal record of the data it describes, data that is enclosed separately in SFDU format. EAST is intended to be human readable as well as to enable automated data interchange between environments that may be heterogeneous. EAST is selected as the language used by a component of a tool that allows users to describe data for reformatting, or to describe data previously formatted, or to describe data before and after conversions between environments. EAST is designed to permit a separation of logical description and physical machine representation in the data description record. The principle is that data is logically the same in different environments, although machine level representations may differ. Extract: Use with scientific data EAST, like its parent, the Ada programming language, is intended to be human readable. The description for a set of data points is divided into two parts: a logical description and a physical description. The logical description “package” is a structured listing of the data points, ordered as occurs on the medium on which it is found. The logical description also must give the exact bit-length of each element of data, which is required to be contiguous on the media. The relation to the hardware/system stops here in the logical part, and it is picked up in the physical description “package”. The Ada term “package” is used because the two parts are syntactically in two separate Ada units called “packages”. It is not recommended that the physical description package be human-read. It is, in any case, more easily decipherable to someone who did not write the description than most other languages would be, save for the natural languages, which have the problem of having less specificity and consequently more ambiguity. The idea is that the readability would help the consumer of the data to understand its type and structure, if need be. EAST permits the provider of the data to describe it without having to learn programming, with use of currently available tools. For a scientist, this may mean better data understanding, especially when it is desireable to examine specific data points in detail. Additionally, to support integration testing, data can be generated and provided to testers in specified, well documented formats. Extract: Use with other data There are numerous examples to show how EAST is used with ancillary data, data that gives the state of the spacecraft or instruments at the time the primary data of interest is observed. Examples 4 and 5 (taken from Reference 3) show how logical and physical packages in EAST may be used to describe ancillary data such as state position, velocity, and inclination shown. http://www.ssd.rl.ac.uk/ccsdsp2/ann00/rdleast.doc |