RDL(ID:8126/)for Record Defnition Language language for describing scientific data structures, part of the ASIST system (together with STOL) References: RDL is a language developed for ASIST for data point interpretation within telemetry packets. ASIST is a real-time, language driven command and control system that is mission adaptable. ASIST receives telemetry data, enabling a user to access the telemetry data online, read the data, and make calibrations. Telemetry data is received in the CCSDS source packet format and is placed in ASIST's memory in a Current Value Table (the CVT) for access. RDL, or Record Definition Language, is a language that is used to describe the precise format of the contents of the Current Value Table. Reports on the telemetry data can be generated, or the data can be read directly to a window. With another language, STOL, System Test and Operation Language, developed for the ASIST on-line user interface, the user interactively picks out the data points, by using mnemonics put in the RDL, to display the data. Mnemonics are defined in ASIST as a telemetry point name. Extract: Use with scientific data In ASIST there is data called psuedo-telemetry, where equations are executed and new data points are generated. These data points may be digital to analog conversions or calibrations to engineering units, a human understandable data form. Conditional and do-loop statements are used to generate event driven (such as when a packet is received with a specific Application Process Identifier or APID) telemetry or periodic psuedo-telemetry. The Current Value Table is divided into two parts, one for the raw telemetry and one for the data with pseudo-telemetry added. The raw telemetry may be archived and may later become playback data. The files containing the RDL that describe the data are usually archived to a database directory. Directives BLOCK, LOCAL, STATEMACHINE, WHEN, DO (loop), IF, FOR, WHILE are useful for generating pseudo-telemetry data points. EQUATION=BLOCK statements can be formed, where the BLOCK is a series of assignment statements and/or conditional directives. Expressions in RDL can include operators +, -, *, /, MOD, REM, **, & (for string concatenation) borrowed from STOL or built-in functions such as trigonometric, standard deviation, variance, and quality of 2(expression based on data points) that are also defined in STOL. Extract: Use with scientific data RDL is not intended for use with science data. Two reasons are apparent: first, the form of science data is often represented in arrays or in an instrument dependent form. And because of the large amount of data or the dependency on hardware architecture, is best handled by a processor that inverts the instrument data, or by a format such as FITS(2) or CDF(3) that will handle large amounts of data in one transfer. There are exceptions, where the science data does not fit into the above categories or is to be handled as engineering data. In addition, interfaces can be written in the RDL or STOL to write the data to files with transport data formats, including CDF (see Database interface section below). Another restriction comes from the semantic capability of the language. RDL keywords are intended for use with engineering data and are not generally intended to describe science data or its attributes. Extract: Use with other data RDL is used to describe data that contains commands sent to a spacecraft or to describe telemetry received from a spacecraft. The spacecraft may be in a pre-launch test mode or may be in full operation. A direction that ASIST is taking is permitting data points in CVT to be changed only in test mode, to permit more complete testing for mission integration. A basic tenet of ASIST is that it does not change any telemetry data values. http://www.ssd.rl.ac.uk/ccsdsp2/ann00/rdleast.doc |