XTCE Lessons Learned

Some of them…Kevin Rice NASA/GSFC

Fall 2013 CCSDS

A Really Brief History• What is it?

– An XML XSD for describing typical ground “database” info• Telemetry mnemonics and properties

– Bit/byte order, units, cals, limits, various data types

• Telemetry Packets or Minor Frames– Including identifying info

• Commands, Arguments, Command Packets/Frames, etc…• Front-end processing info• Algorithms• Services

• What do you do with it?– Intended as a neutral exchange format for mission ops. databases -- possibly used as a “native” format if the

tools supported• Published, versions?

– OMG own/controls/publishes XTCE– XTCE 1.0 (2005), XTCE 1.1 (2008), XTCE 1.2 (In process?)– And CCSDS “co-publishes

• Success Stories?– Pretty much prototyped by “everyone”– Many vendors support in various ways (US)– “Flown” on station and at least one DoD Sat– Continues to show popularity in the greater community

Lesson Learned

• Without going into the syntactic weeds– We’ll look at a few things we did right– And a few things we could have done better

• Note: – Probably not comprehensive– And somewhat subjective

The Good• Schema types reasonably well defined, re-used and consistent throughout

the schema– Mostly clean output from say a JAXB… mostly.

• Came close to the “90%” solution we were aiming for w/tlm & cmd– I would venture this one item is typical in the industry but missing: range enumerations– Almost everything else asked for is just not quite universal… not that it shouldn’t

necessarily be there

• Concept never questioned & consistently popular – Definitely true for customers (e.g. NASA)– Never heard a vendor say it was a bad idea…

• Good Marketing & Champion(s)– GSAW, GSAW Tutorial Sessions, SpaceOps, CCSDS and OMG special days and tutorials– Dan Smith

• Ultimately pretty good documentation– 2 Green Books

The Bad• Failed to fully annotate intended meaning of every tag and attribute• Examples at publication time were insufficient for most people

– People wanted real examples, free/open software and documentation• No forum…• Issues tracking doesn’t have “front-end” triage

– A lot issues piled up, many just “junk”– (something of an OMG problem)

• Schema– Is ambiguous in places– Is over-generalized in places– Has areas few want to implement

• Parallel development during creation not comprehensive enough

The Ugly

• Failed to anticipate push back from some vendors• Failed to appreciate customers often don’t know how

their tlm/cmd systems work who are tasked specifically w/using XTCE– They are use to going to their vendors and contractors

• Failed to appreciate that the standards community is relatively inflexible at revision once published…

• A few tags were not done well and it should have been obvious to us:– Arrays and units