The ArcPad Team Blog

Unofficial stuff from the team behind the World's leading mobile GIS platform

Wednesday, June 18, 2008

What is an ArcPad AXF?

ArcPad 7.1 has delivered a lot of new capabilities, many of which, such as the 'related tables', come from strengthened support of ArcGIS's Geodatabase capabilities in the mobile environment.

Prior to ArcPad 7.1, shapefiles were ArcPad’s most common spatial file format for features. Shapefiles are great for many applications, but shapefiles lack the capabilities to support more sophisticated relational database requirments that exist in the ArcGIS Geodatabase. So ArcPad 7.1 introduced the AXF format, which we like to refer to as a "lightweight geodatabase".

Not a new File Format

Now before you groan "Oh no not another spatial file format", like the ArcGIS Geodatabase, AXF is not actually a new file format but rather it is built on top of existing proven database technology. In this case, AXF is built on top of Microsoft's SQL Server Compact Edition (SQLCE).

SQLCE has been evolving for several years and has strengthened to become a powerful and robust database technology. Although in many ways it is the very little brother to the full Microsoft SQL Server, it has the distinction of being multi platform, being available for Windows CE and Windows Mobile operating systems as well as Windows and Windows Vista for the desktop. This includes the SQLCE database files themselves also being fully portable. You can create them on one platform and use them on another, exactly the sort of capability the multiplatform ArcPad system needs in a file format.

So how do AXF files work?

In the most simplistic terms, you might consider an AXF as a collection of shapefiles in a database. Where attributes in a shapefile are stored in a DBF, the equivalent attributes in AXF are just columns in tables. The ‘shape’ for each feature is stored in special spatial BLOB column, the contents of which are exactly as you would find in a shapefile’s .SHP file. The AXF schema, which describes to ArcPad how spatial data in the AXF database is organised, also stores metadata associated with each layer, including the projection details and layer definition containing symbology, forms and scripts.

A cool thing to note at this point, that where a customised collection of shapefiles might end as quite a few files, a collection of layers in an AXF remains a single file. This makes it much easier to move data around without the worry that one of the shapefile components gets lost which is of particular benefit in mobile environments where field users are sending back data files via email and only have to worry about a single file.

Integration with the ArcGIS Geodatabase

The power of the AXF “lightweight geodatabase really kicks in when you start to exploit the features of the ArcGIS Geodatabase in your organisation, in particular domains, sub types and relationships.

The ArcPad Data Manager and ArcPad Geoprocessing tools, automatically translate ArcGIS’s Geodatabase rules into AXF. This can result in significant benefits as you can design your rules in the Geodatabase and “just have them work” in the field with ArcPad, with almost no special customisation required.

If you want to customise your AXF further with forms and scripts, you can do so with ArcPad Studio in almost the same way as you can do it for shapefiles. You can create forms and scripts, all of which get ‘imbedded’ in the AXF along with the spatial data.

Workflow Benefits

The tight coupling of the AXF “lightweight geodatabase” with the ArcGIS Geodatabase has been designed to improve the whole enterprise --> field --> enterprise workflow cycle.

As your organisation builds rules in the enterprise geodatabase, these rules automatically become part of the field workflow with ArcPad, leading to higher quality data capture and maintenance in the field. Domains and subtypes automatically become ‘drop down’ menus for efficient and less error prone data input. This then in turn leads to less data maintenance effort when checking field data back into the enterprise geodatabase.

Further reading and information

This has only been a brief description of the AXF.

At the DevSummit this year in Palm Springs, we covered some more detail and you can see/listen to this online.

There is a recent podcast covering a little on AXF.

At the forthcoming User Conference in San Diego, we will be presenting information in many more scenario contexts ranging from the more simple benefits, ArcGIS Geodatabase integration, workflow improvements and leveraging more through further customisation and the power of the SQLCE engine.

We will also expand on how ArcPad is going forward with AXF and integrating ArcPad field workflows directly with ArcGIS Server.

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