Difference between revisions of "Protege4ClientServer"
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Revision as of 17:02, October 24, 2012
Contents
Introduction
These are some pages under development to document the Protege 4 Server. We are hoping to release an early alpha soon.
What is it?
The Protege OWL Server provides a platform for collaborative editing and version control of a collection of ontologies. The Protege server tracks changes made to its ontologies, enforces an access control policy for its documents and checks for conflicts between its clients. When used with the Protege client, ontology editors can view and modify a shared ontology in parallel. If a editor chooses, the editor can watch changes made by other editors as they occur. To change an ontology, an editor first makes the changes in his local copy of the ontology. When he is happy with his changes, he can commit them making them available to other editors of the ontology. Alternatively, an editor making changes to his local copy can save his copy of the changes and commit them in a later session.
In addition, the Protege OWL Server can be used as something more like a simple version control system. We are developing a set of command line tools that will be able to use a Protege OWL Server to provide such traditional version control services as checkn, checkout, update, commit and history query commands. The Protege 4 client can be used in this manner as well: an ontology editor can choose not to turn on auto-update and make all his updates and commits manually.
Comparison with the Protege 3 Server
There are several differences between the Protege 3 Server and the Protege 4 Server:
- The local copy.
- In Protege 3, when a client connect to the server, any change made to the client is immediately reflected on the server. In Protege 4, in contrast, changes only get propagated to the Protege server when the user commits the change. This allows a user of a Protege client to consider his changes before sending the changes to the server. This is a significant enough concept that we describe it in more detail below.
- Decoupled client-server.
- In Protege 3 when the server goes down or the network is interrupted, the Protege 3 client either freezes or crashes. In contrast, in Protege 4, if the server stops or is inaccessible, the Protege client continues running normally. It is only when some server operation is attempted, such as an update or commit, that the user may become aware that there is a problem communicating with the server.
- Commit granularity.
- In Protege 3, changes are sent to the server as they are made. In Protege 4 a collection of changes are only committed when the user is ready the user is able to add a commit comment describing the nature of the changes.
- Optional automatic update.
- In Protege 3, a user sees edits from other users as they occur. In Protege 4, this is optional.
The Local Copy/Sandbox
With the Protege 4 client server, when a user checks an ontology out from the server, he gets a separate copy of the server ontology. The user can then modify this copy in any way that he likes and the changes will not go to the server until the user commits the changes.
In fact this local copy can be saved to disk and then even editted with a different editor than Protege before it is committed to the server. Specifically, a user can
- start protege and load an ontology from the server,
- save the ontology somewhere on the local disk,
- exit protege and edit the ontology with a text editor
- restart protege and open the ontology from disk
- commit the changes which will include the changes made with the text editor.
What happens is that when the file is saved, Protege also saves some files containing the server providing the ontology document, the location of the document on the server and the revision of the ontology document on the server. So if I save an ontology as Thesaurus-redmond.owl in the client.ontologies directory then Protege saves the following files:
- client.ontologies
o Thesaurus-redmond.owl
- .owlserver
o Thesaurus-redmond.owl.history
o Thesaurus-redmond.owl.vontology
The Thesaurus-redmond.owl.vontology contains information that describes the relationship between the ontology in Thesaurus-redmond.owl and the document on the server. The Thesaurus-redmond.owl.history contains a local cache of the history of changes made to the ontology document on the server. It is not required - if it is deleted it will be rebuilt - but it provides significant performance advantages for the client especially in the case where either the network is slow or the ontology is large.
Videos
Here is the first of several videos that I am going to make to demonstrate server features:
- Protege OWL Client-Server Basics. This video shows how to
- access a server,
- upload an ontology,
- follow changes made by another user with auto-update,
- have an extended session with the server spanning multiple Protege sessions.
Large ontologies on a slow network
When a large ontology is being uploaded or downloaded from a server on a slow network, it can take a while to transfer all the necessary data. Unfortunately we have not yet determined how to best monitor and report the progress of this operation so the user doing the upload/download will have little indication of the progress. The good news here is that the user only needs to experience this once for the initial upload of the ontology to the server and once for his initial download of the ontology. In addition, since the upload of an ontology is a one time thing, it is very likely that it can be performed on a faster network.
The issue concerns the change history stored on the server representing the set of changes between revision 0 and revision 1. These changes consist of the full set of changes needed to create the initial version of the ontology. Thus for instance, if the NCI Thesaurus is uploaded onto the server, the set of changes to go from revision 0 (the empty ontology) to revision 1 (the initial version of the Thesaurus on the server) will contain over 1.2 million individual changes. This change set is stored in a 300 MB file which then needs to be transfered to any client that wants a copy of the ontology. (In point of fact, this change set gets compressed before it hits the network so the actual data copied across the wire is only about 44 MB.)
Once the ontology is downloaded to the client, the client can save the ontology with the change history to disk for later reference. When the ontology is reloaded from the disk, the client will already have a copy of the 1.2 million changes from revision 0 to revision 1 and will not need to download it again from the server.
