Creating a query in Netgraph
Searching a corpus is one of main purposes of the corpus. Netgraph is a tool especially designed and developed for searching PDT 2.0.
Netgraph is a client-server application that allows multiple users to search PDT 2.0 on-line and simultaneously through internet. Netgraph is designed for making the search as easy as possible and still keeping the power of the query language strong enough.
Netgraph consists of two parts - a server and a client. The parts communicate to each other through internet. The server searches the treebank (the server and the treebank are located at the same computer). The client serves as a front-end for users and may be located at any node in internet. It communicates with the server, sends queries to it and receives results from it. It is possible that both the server and the client be at the same computer.
Netgraph server is written in C and C++ and works smoothly on Linux, other Unix-like systems, and Apple Mac OS. (An experimental version exists for MS Windows, too.) It requires the treebank in 'fs' format, encoded in UTF-8. Netgraph server allows setting user accounts with various access permissions.
Netgraph client is written in Java and is platform-independent. It exists in two forms - as a stand-alone Java application (which is full-featured and needs to be installed first, along with Java 2 Runtime Environment), and as a Java applet (which provides full search power and runs in a web browser without installation; it requires Java 2 plug-in installed, though).
A query in Netgraph in general is a subtree which should be included in result trees. Searching the corpus means searching for trees which contain the query as a subtree. This simple definition is extended using so called meta-attributes in order to allow setting much more complex queries. The meta-attributes allow setting transitive edges, optional nodes, position of query nodes in result trees, size of result trees, order of nodes, relations between attributes at different nodes in result trees, negation, and many other things.
Queries in Netgraph are created user-friendly using a graphic environment. An example of such a query is in the picture:
In this query, we are interested in all trees containing a node evaluated as predicate and governing at least three nodes evaluated as actor, effect, and addressee. We do not set any condition on the order of the nodes.
One of the results (sent back by the server) may be:
The nodes matching with the query are emphasised by yellow and green color. As you can see, the predicate in the result has got more sons than we have specified in the query. It is in accordance with the definition of searching in Netgraph - the query tree is only included in the result tree as a subtree. Also note that the order of the nodes in the result is different from their order in the query. Meta-attributes allow controlling both the real number of sons and the order of nodes, if required.
For more information about Netgraph, read the Netgraph client manual or see the Netgraph home page.
For information about how to install Netgraph, see quick installation instructions for Netgraph client and quick installation instructions for Netgraph server. You should also read the Netgraph Client Manual and the Netgraph Server Installation Manual.
Please note that you only need to install Netgraph server if you want to search your own tree corpus. For searching PDT 2.0, a powerfull Netgraph server is provided by Institute of Formal and Applied Linguistics at quest.ms.mff.cuni.cz on port 2200. It is accessible for anonymous user via internet and you can connect to it using Netgraph client. If you want a full non-anonymous access to the server, please contact the author of Netgraph at mirovsky@ufal.mff.cuni.cz.
For more information and for news, do not forget to visit the Netgraph home page.
