GF online editor for simple multilingual grammars

[GF online editor screen shoot]


Traditionally, GF grammars are created in a text editor and tested in the GF shell. Text editors know very little (if anything) about the syntax of GF grammars, and thus provide little guidance for novice GF users. Also, the grammar author has to download and install the GF software on his/her own computer.

In contrast, the GF online editor for simple multilingual grammars is available online, making it easier to get started. All that is needed is a reasonably modern web browser. Even Android and iOS devices can be used.

The editor also guides the grammar author by showing a skeleton grammar file and hinting how the parts should be filled in. When a new part is added to the grammar, it is immediately checked for errors.

Editing operations are accessed by clicking on editing symbols embedded in the grammar display: +=Add an item, ×=Delete an item, %=Edit an item. These are revealed when hovering over items. On touch devices, hovering is in some cases simulated by tapping, but there is also a button at the bottom of the display to "Enable editing on touch devices" that reveals all editing symbols.

In spite of its name, the editor runs entierly in the web browser, so once you have opened the web page, you can continue editing grammars even while you are offline.

Current status

At the moment, the editor supports only a small subset of the GF grammar notation. Proper error checking is done for abstract syntax, but not (yet) for concrete syntax.

The grammars created with this editor always consists of one file for the abstract syntax, and one file for each concrete syntax.

Abstract syntax

The supported abstract syntax corresponds to context-free grammars (no dependent types). The definition of an abstract syntax is limited to Available editing operations: Error checks:

Concrete syntax

At the moment, the concrete syntax for a language L is limited to Available editing operations: Also, Error checks:

Compiling and testing grammars

When pressing the Compile button, the grammar will be compiled with GF, and any errors not detected by the editor will be reported. If the grammar is free from errors the user can then test the grammar by clicking on links to the online GF shell, the Minibar or the Translation Quiz.

Grammars in the cloud

While the editor normally stores grammars locally in the browser, it is also possible to store grammars in the cloud. Grammars can be stored in the cloud just for backup, or to make them accessible from multiple devices.

There is no automatic synchronization between local grammars and the cloud. Instead, the user should press [Cloud Upload] to upload the grammars to the cloud, and press [Cloud download] to download grammars from the cloud. In both cases, complete grammars are copied and older versions at the destination will be overwritten. When a grammar is deleted, both the local copy and the copy in the cloud is deleted.

Each device is initially assigned to its own unique cloud. Each device can thus have its own set of grammars that are not available on other devices. It is also possible to merge clouds and share a common set of grammars between multiple devices: when uploading grammars to the cloud, a link to this grammar cloud appears. Accessing this link from another device will cause the clouds of the two devices to be merged. After this, grammars uploaded from one of the devices can be downloaded on the other devices. Any number devices can join the same grammar cloud in this way.

Note that while it is possible to copy grammars between multiple devices, there is no way to merge concurrent edits from multiple devices. If the same grammar is uploaded to the cloud from multiple devices, the last upload wins. Thus the current implementation is suitable for a single user switching between different devices, but not recommended for sharing grammars between multiple users.

Also note that each grammar is assigned a unique identity when it is first created. Renaming a grammar does not change its identity. This means that name changes are propagated between devices like other changes.

Example-based grammar writing

This is work in progress...

Future work

This prototype gives an idea of how a web based GF grammar editor could work. While this editor is implemented in JavaScript and runs in the web browser, we do not expect to create a full implementation of GF that runs in the web browser, but let the editor communicate with a server running GF.

By developing a GF server with an appropriate API, it should be possible to extend the editor to support a larger fragment of GF, to do proper error checking and make more of the existing GF shell functionality accessible directly from the editor.

The current grammar cloud service is very primitive. In particular, it is not suitable for multiple users developing a grammar in collaboration.

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Last modified: Fri Oct 7 14:06:14 CEST 2011