Keywords: linedb

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## Queries

The new server supports TAP-VAMDC queries using VSS1 or VSS2 languages. The query may be as simple as:

      select *

to retrieve the whole database, or for example

      select * where
      (RadTransFrequency >= 9.671000e+04 and RadTransFrequency <= 9.677000e+04) and
      RadTransProbabilityA >= 3.000000e-06 and
      InChiKey in ('TXKMVPPZCYKFAC-UHFFFAOYSA-N','OKKJLVBELUTLKV-UHFFFAOYSA-N')

to retrieve the S2O and CH3OH lines (`InChIKey`), between 96710 and 96770 MHz (`RadTransFrequency`), which have an Einstein coefficient above 3e-6 (`RadTransProbabilityA`). Once the query command is built, it is encoded in the whole HTTP url.

The list of supported restrictables (i.e. the parameters which can be used for filtering) can be found in the VAMDC documentation1. For interfacing with the command `SELECT`, LINEDB uses the restrictables shown in the Table 1. `RadTransFrequency` and `RadTransProbabilityA` are direct equivalent of the `SELECT` filters. There is no restrictable for selecting a line by its upper level energy (`/ENERGY`), so the filtering is performed internally in LINEDB afterwards.

The `/SPECIES` case is a more complex issue. LINEDB uses the molecule formula or name to identify a species. The equivalent in the XSAMS format is the `OrdinaryStructuralFormula` (see subsection 3.3 for details). However, because this property can be an ambiguous reference to a species (e.g. ``Methanol'' and ``CH3OH'', ``HCCCN'' and ``HC3N''), it can not be used as a filter. VAMDC offers instead the InChI (IUPAC International Chemical Identifier2) or the InChIKey (hashed InChI) as non-ambiguous identifier. In practice, LINEDB has to know how to translate the formula as an InChIKey. This is done by downloading and parsing the full `Species` table (and only this one) once at the beginning of the session. As of today this table provides 734 species; they are listed in the Appendix C.

Table 1: Look-up-table between the LINEDB `SELECT` options and the VAMDC restrictables.
`SELECT` option | Restrictable | Comments
`/SPECIES` | `InChIkey` | Translation needed
`/FREQUENCY` | `RadTransFrequency` | [MHz]
`/ENERGY` | N/A | Done internally in LINEDB
`/AIJ` | `RadTransProbabilityA` | []
`/ORIGIN` | (not relevant) |
`/SORTBY` | (not relevant) |
`/EPSILON` | (not relevant) |

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