Use Case:  Associate Projects for Multi-Frequency Studies.

ALMA will be used to observe (molecular) lines in different transitions. These transitions being far enough from each other in frequency they will be observed at different epochs with different antenna configurations. The physical interpretation of the data requires common angular and spectral resolutions. The purpose of this Use Case is to demonstrate the possibility to associate archived data from different projects and generate an ObservationUnit including the adequate data for processing and subsequent analysis.

Goal: Invoking the archive, generate an ObservationUnit with the intent to combine data at different frequencies.

Contact Author:   F.Viallefond

Priority: Very desirable

Frequency:  Few times a week.

Preconditions: 

1. Database is running
2. User got authenticated
3. The coordinates of the position(s) of the source are known.
4. The name of the line(s) with transitions to be associated are known.

1. Connect to the ASA via ACS from the home institute
   Alternate Course: none
   Exception Course: Connection can't be established: try again until timeout.
   Postcondition: Connection established.
2. Amongst the available services listed when the connection is established, select the service which allows to create an ObservationUnit; this opens a GUI for an interactive high level interface which maps user request into XPath queries.
   Alternate Course: select an interface to submit a script for batch mode request
   
3. In case of interactive mode, from the GUI, select the source, the line(s) of interest and the different transitions. Step by step selections could assist the user, e.g. for a given source and molecule the GUI leaves the choice on transitions only for those which have been observed. For requests of data being scheduled but not yet observed or private data when the ASA user has no permission access, a message has to inform the status of these peculiar data .
   Alternate Course: for batch mode the user selection is provided in the submitted script
   Exception Course:
   • an attribute for selection is rejected because of bad user input (e.g. bad syntax for coordinates); an on-line help is available; try again until proper synthax is provided.
     
   • no entities matching with the selection; the user is informed via comprehensive messages, e.g. transition unknown, no entities for that transition, no entity for that source etc...; quit button allows the user to exit and close the connection.
     Alternate Course: for batch mode requests the message is sent to the ASA user via email.
     
4. The list of available data is provided with informations such as the rms noise level, the angular and spectral resolutions, the extend of the region observed in case of mosaicing, the availability or not of auto-correlation measurements, the availability or not of ACA short spacing measurements; whether such type of association for that source have already been done in the past by the ASA user community.
   Alternate Course: for batch mode requests this information is sent by email to the actor.
   
5. In case of mosaicing select the region corresponding to the intersection of the regions which have been observed in the different lines/transitions. For single-field observations select the field.
   Exception Course: no spatial overlap; a quit button allows the user to exit and close the connection. For batch mode the message is sent by email to the actor.
   
6. Select the lowest angular resolution amongst the listed values and select the lowest velocity resolution.
   This provides anticipated rms noise levels in brightness temperature and/or Jy/beam for that common spatial and spectral resolution.
   
7. Satisfied with the data selection and the anticipated levels of sensitivity?
   no: offer the possibility for the user to modify selection criteria
   yes: inquire
   
   • to make DataCollections (probably one per line transition) including, mandatory, the visibilities with the associated calibration parameters.
     N.B.: not all visibilities may be required! only those suitable for the requested angular resolution are selected.
     
   • to make the association of the DataCollections for producing an ObservationUnit.
     Alternate Course: inform by email that an ObservationUnit has been created and is available up to some expiration date, either to retrieve them or to process them at the RSC provided the user submits a reduction script. This information by email could come with a suggested processing script to be checked and eventually modified, if necessary, by the user. Suggested scripts would come only in case of standard modes (TBD) or if scripts for associations of similar type have already been used sucessfuly in the past. These scripts may take advantages related to the nature of the association to use specific methods such as a joined deconvolution of the observations at the different frequencies, as that could be appropriate in the present case for some scientific applications.
8. Offer to the user 3 possibilities:
   1. retrieve the ObservationUnit either via internet (before some expiration date) or on some standard (TBD) media in the standard export data format (data format of the DRP supported by ALMA project or VOTable or FITS? TBD)
      
   2. switch to a new service for processing the ObservationUnit at the RSC if the user want to have some control in the sequence of events during the processing.
      Alternate Course: simple standard processing which computing time inexpensive could be done automaticaly using that service in batch mode
      
   3. submit a processing script.
9. In the case the ObservationUnit has been processed at the RSC, the noise level and some other relevant parameter as needed for the resulting images which have been generated. The images are new members in the DataCollecions. Reports (history files) about all events since the beginning of this Use Case become also new members at the relevant levels in the ObservationUnit structure. The ASA user can retrieve the ObservationUnit, with or without the Table members (those which host the visibilities and calibaration parameters) in the DataCollections.
   
10. Archive the result and make protection accesses at the DataColection level as needed.

Postconditions:

1. An ObservationUnit in an adequate format available (for an lapsed time TBD) for reprocessing at the RSC in case alternate processing methods would be desired.
   
2. Images of several lines/transitions at the same spatial and spectral resolutions as members in the data collections of the ObservationUnits.
   

Issues to be Determined or Resolved: