Knowledge Base

The VIALACTEA Knowledge Base (VLKB) identifies a set of data collections, catalogues and services enabling discovery and access on them, all targeted ad the galactic plane and intiailly put together and made available by the EU FP7 VIALACTEA Project.

The VIALACTEA Knowledge Base (VLKB) is a collection of scientific data, stored as relational databases, and web services. The scientific data inside VLKB are accessible through a Virtual Observatory enabled infrastructure through the TAP protocol and the interface is located at this URL:

This page describes the basic usage of the available services, by means of direct calls to the APIs or using common tools that are aware of the used standards.
The VLVA client tools enable to consume the services with specific visual analytics features developed on the galactic research domain.

The services described here are:

How to consume the TAP one will be explained in two ways, using the TOPCAT tool and directly acting on a web interface to the service.
Calls to the dataset dedicated services will be described through the main usage of its HTTP parametric interface (the one that gets hidden to the user and consumed through the VLVA).


Basic service description

TAP is an IVOA Recommendation (a standard interface protocol) that enables programmatic access to relational databases or collections of tabular content, allowing for richer metadata content focused on the astronomy domain requirements.
Services implementing this protocol, and registered in the IVOA Registry of Resources, are usually discovered through their IVOID (IVOA unique identifiers solution). In this developing phase the VLKB TAP is however not registered, thus its access is done by means of its base access URL:

This endpoint, while it could be used to access a basic interface to the service, is the actual programmatic access URL for the TAP service.
The VLKB TAP service provides access to information of catalogue content of the VLKB, from compact sources, to diffuse structures, to numerical SED models and overview of datasets collections (that are served through the VLKB Dataset services described below in this page.

VLKB TAP access using TOPCAT

For a friendly access to the VLKB TAP we suggest to use TOPCAT (TOPCAT) that includes a TAP query dialog.

After you've downloaded and launched the TOPCAT application you should see the TOPCAT main window, where you can click to open the Table Access Protocol (TAP) Query dialog window (see figure below or go through VO -> Table Access Protocol (TAP) Query from the menu).

This will open a new window on your screen (with the Select Service panel visible) where, at bottom, in the Selected TAP Service section, there's the TAP URL text field ready to welcome the base URL for the service.
Input the VLKB TAP base URL in there and click on the Use Service button to move on.

The click will bring you to the Use Service panel of the already opened dialog window where you will find the Metadata section filled with the available catalogue content. At the bottom you will also see an ADQL Text section that will allow you (and help you) fill in the query to the service itself.
As an example, you can select a table in the Metadata section and use the Examples button to browse within the predefined available queries.

This will provide you with a ADQL query you can submit to the service (by clicking on the Run Query button). The result would be a table loaded in the TOPCAT main window where, e.g., clicking on the Display table cell data (or, from menu Views -> Table Data), you can browse and work on the data.

VLKB TAP access directly using the TAP API
(for expert users)

A direct access to the VLKB TAP, without using other tools, is available through its TAP interface, available at the same base URL as the one exposing the TAP standard protocol interface. Simply point your browser at

and use the available links to browse the contents and the ADQL dialog box to enter your ADQL queries, optionally choosing the output format for the results and the choice of synchronous/asynchronous execution of the SQL job.

VLKB Datasets Discovery & Access Services

VLKB Datasets through ReST API
(for expert users)

To obtain FITS datacube access it is posible to use services: search, cutout and merge. Results are returned in form of an XML file, then direct investigation of these datacubes may be done by accessing the URL via a web browser or command line tool capable of HTTP connections (like, e.g., curl). These services were not designed to be handled interactively by the user, but rather by scripting tools, or programming languages.

For example to perform a search in the sky circular area of radius 0.1 centered at galactic coordinates [l,b] = [10,0] one would type into the browser:

and, assuming the user is authenticated, result is in XML as above.

The typical URL pattern of those services uses the requested <function> and related parameters list <paramlist>:

The available services are: vlkb_search, vlkb_cutout and vlkb_merge.
The available query parameters in key=value pairs are described in table: