A typical ODF/SDF directory contains several dozens of files. The purpose of each file can be identified from a combination of file name and content of the FITS header.
The filenames associated with ODFs and SDFs consist of up to 27 characters, followed by a '.' (dot), followed by 3 characters. All characters are upper case. The adopted naming convention is as follows:
This encoding uniquely specifies the instrument, the type of observation (scheduled or unscheduled), the exposure number, the CCD/OM window identifier, the file type, and the format. Descriptions of the each filename field are listed in Table 1.
| Field | Description | |
|---|---|---|
| RRRR | The revolution (orbit) number | |
| obsidentif | The observation identifier, 10 digit: PPPPPPOOLL | |
| PPPPPP | the identifier of the proposal that contains the obs. | |
| OO | identifier of the observations within the proposal | |
| LL | extended identifier (usually 01) | |
| Notes: | For slews the first of the six P is '9' | |
| For pseudo ODF components of mosaic pointings, the values of LL | ||
| assume values (30+x), where x is the number of the mosaic pointing. | ||
| II | The instrument, or data source, identifier | |
| OM | optical monitor | |
| R1 | RGS-1 | |
| R2 | RGS-2 | |
| M1 | EPIC MOS-1 | |
| M2 | EPIC MOS-2 | |
| PN | EPIC PN | |
| RM | EPIC radiation monitor | |
| SC | Spacecraft | |
| U | ||
| S | Indicates that the observation was scheduled | |
| U | Indicates that the observation was unscheduled | |
| X | not applicable (because not science files) | |
| EEE | The exposure number within the observation | |
| 000 | file does not correspond to an exposure period | |
| 9XX | is used for diagnostic Q dumps (RGS spectroscopy+Q) | |
| CC | The CCD identifier/OM Window identifier (2 digits) | |
| EPIC MOS CCD number (1-7) & CCD read-out mode (0,1) | ||
| EPIC PN CCD number (01-12) | ||
| RGS CCD number (01-09) | ||
| Note: ``00'' is used for multi-CCD files | ||
| OM science window identifier | ||
| 00 | used for those files not having a corresponding CCD or science window | |
| MM | The data contained within the file name | |
| AT | Spacecraft attitude | |
| AU | EPIC or RGS auxiliary | |
| BU | EPIC PN burst | |
| CC | EPIC counting cycle report (auxiliary file) | |
| CI | EPIC MOS compressed timing | |
| D1 | DPP non-periodic Housekeeping | |
| D2 | DPP non-periodic Housekeeping | |
| DI | EPIC MOS or RGS diagnostic | |
| DL | EPIC PN discarded lines data | |
| DP | RGS Digital Pre-Processor non periodic housekeeping | |
| EC | EPIC MOS extra heating configuration non-periodic housekeeping (if II=M1 or M2) | |
| EC | EPIC Radiation Monitor (ERC) count rate (if II=RM) | |
| En | OM engineering where  |
|
| ES | EPIC Radiation Monitor (ERC) spectra | |
| FA | OM fast | |
| HB | EPIC high bit rate interface buffer size non-periodic housekeeping | |
| HC | EPIC high bit rate interface configuration non-periodic housekeeping | |
| HT | EPIC MOS high bit rate interface threshold values non-periodic housekeeping | |
| HT | RGS high time resolution | |
| IM | EPIC or OM imaging | |
| NO | EPIC PN noise data | |
| NP | OM non-periodic housekeeping | |
| OF | RGS offset file | |
| OD | EPIC PN offset data | |
| OV | EPIC MOS offset / variance | |
| P1 | Spacecraft housekeeping 1 periodic housekeeping | |
| P2 | Spacecraft housekeeping 2 periodic housekeeping | |
| P3 | Spacecraft Attitude 1 periodic housekeeping | |
| P4 | Spacecraft Attitude 2 periodic housekeeping | |
| P5 | Spacecraft SYS_HK_SID0 periodic housekeeping | |
| P6 | Spacecraft SYS_HK_SID1 periodic housekeeping | |
| P7 | Spacecraft SYS_HK_SID4 periodic housekeeping | |
| P8 | Spacecraft SYS_HK_SID5 periodic housekeeping | |
| P9 | Spacecraft SYS_HK_SID6 periodic housekeeping | |
| PA | EPIC PN additional periodic housekeeping | |
| PA | OM priority field acquisition (auxiliary file) | |
| PC | RGS CCD temperature periodic housekeeping | |
| PF | RGS full periodic housekeeping | |
| PF | OM priority fast (auxiliary file) | |
| PM | EPIC PN main periodic housekeeping | |
| PT | EPIC MOS bright pixel table non-periodic housekeeping | |
| PE | EPIC MOS or OM periodic housekeeping | |
| RA | Raw Attitude file | |
| RF | OM reference frame (auxiliary file) | |
| RI | EPIC MOS reduced imaging | |
| RO | Spacecraft reconstructed orbit | |
| SP | RGS spectroscopy | |
| SU | Summary information | |
| TC | Spacecraft time correlation | |
| TH | OM tracking history (auxiliary file) | |
| TI | EPIC timing | |
| TM | EPIC thermal monitoring limits non-periodic housekeeping | |
| WD | OM priority window data (auxiliary file) | |
| F | The file type | |
| E | event list file | |
| I | image file | |
| X | auxiliary file | |
| H | housekeeping | |
| S | spacecraft | |
| M | summary | |
| ZZZ | File format (3 characters) | |
| ASC | ASCII file | |
| ASZ | Compressed ASCII file | |
| FIT | FITS file | |
| FTZ | Compressed FITS file | |
| SAS | SAS output (not original ODF constituents) | |
The nature of science ODF/SDF FITS files can also be identified by inspection of the value of the respective binary table(s) extension. This coding is described in Table 2. The Unix convention to indicate multiple files is used; e.g.: M[1,2]IME1 means M1IME1 (MOS1) and M2IME1 (MOS2).
| File type | BINTABLE ... |
| MOS Imaging Mode Event List File | M[1,2]IME1 |
| MOS Timing Mode Event List File | M[1,2]TIE1 |
| MOS Auxiliary File | M[1,2]AUX1 |
| MOS Periodic Housekeeping File | PERIODIC_HK |
| PN Imaging Mode Event List File | PNIME1 |
| PN Timing Mode Event List File | PNTIE1 |
| PN Burst Mode | PNBUE1 |
| PN Auxiliary File (first extension) | PNAUX1 |
| PN Auxiliary File (second extension) | PNAUX2 |
| PN Housekeeping (first file) | PERIODIC_HK |
| PN Housekeeping (second file) | MAIN_PERIODIC |
| RGS Spectroscopy Mode Event List File | R[1,2]SPE1 |
| RGS High Time Resolution Event List File | R[1,2]HTE1 |
| RGS Auxiliary File (first extension) | R[1,2]AUX1 |
| RGS Auxiliary File (second extension) | R[1,2]AUX2 |
| RGS Periodic Housekeeping Files | PERIODIC_HK |
| OM Imaging Mode Image File | OMIMI1 |
| OM Fast Mode Event List File | OMFAE1 |
| OM Tracking History Data Auxiliary file | OMTHX1 |
| OM Reference Frame Auxiliary File | OMRFX1 |
| OM Periodic Housekeeping File | OMPEH1 |
| OM Non-Periodic Housekeeping File | OMNPH1 |
| Spacecraft Attitude History File | SCATS1 |
| Spacecraft Time Correlation File | SCTSC1 |
Finally, the nature of a file can also be identified by the value of the keyword DATATYPE in the binary table header (see Table 3), although in this case only the file type can be unambiguously determined, whereas a degeneracy in the instrument remains.
As mentioned above, the housekeeping files cannot always be uniquely distinguished from their binary table extension. However, they can still be recognised by their file names.