Technical Overview of XML Framework for Algorithm Innovation - XFAI

The XML Framework for Algorithm Innovation is a tool for researchers to create,
run and deploy scripts to simulate distributed sensor networks. At its core is Water, a general purpose programming language using XML syntax. A general purpose language is needed because complex networks that may dynamically configure
themselves need arbitrary processing capabilities. Without them too many 'good ideas' simply become unimplementable.

Since Water uses XML syntax, it meshes better than other languages with data in XML format allowing both dynamic and static data to be interspersed for complex knowledge representation. Water has web services integrated in, facilitating the sharing of data AND code across Internet-connected computers.

XFAI is built on top of Water to create an environment to help researchers develop and share software. By making it easy for researchers to see each other's code,
make new versions of it, and incorporate existing scripts within new scripts, each researcher can easily leverage the work of other researchers regardless of their location.

The XFAI browser interface can be run on any computer connected on the network with the XFAI server. This can be a private network or the Internet itself. This server-browser pair of computers can be physically on the same computer or spilt between two different machines. The simplest configuration is to run the XFAI server on the same computer that is running the browser user interface. This allows you to run "stand-alone" without a network connection.

The XFAI interface facilitates the running of scripts in several ways. First, a script may be selected from the menu of scripts served by a particular XFAI server. Second, the source of any script deployed on any connected XFAI server can be brought into the source code pane, modified and executed. Third, the 'view' of the source of a script can be changed from textual 'code' into 'buttons', a GUI representation of the script that hides code details while exposing variables that can be modified and automatically inserted into the script code. The button view allows an intermediate functionality between a no-modifications 'just run it' mode and the full power to edit all of the code.

Finally XFAI scripts can be run programmatically. Data can be retrieved from a third computer, that is, one other than those running the server or browser, and that data can be passed to a script on a fourth computer. XFAI's 'execute' command allows a script to come from one computer yet run on another. Since XFAI employs a general purpose language, any number of 'execute' commands can be embedded in a single script. Intervening 'glue' code can be written to flexibly patch a software network together to run a complex simulation. Since 'execute' is, syntactically, just another Water method. There is no language barrier to employ it in a wide variety of situations within a script.

In addition to Water, XFAI can also run MATLAB code via its embedded 'Octave Server'. Octave is an open source version of a MATLAB engine. MATLAB can be run directly by typing it into the source pane and clicking on the "Execute MATLAB" button. It can also be run programmatically via the 'execute' method. Execute takes a string of source code as its main argument. That can either be a file name containing source or the actual source itself. In addition to the 'execute' parameters that let you indicate which computer the code lives on and which computer it should be run on, there is also a parameter to indicate the language that the source is written in. A present, XFAI supports two languages, Water and MATLAB. the default value of the Source_language parameter to 'execute' is "guess" meaning let XFAI figure out from examining the source, what language it is in. Usually XFAI guesses right, but you can declare the language to ensure success if you like.

XFAI has three presentations of a script. The shortest, is simply the name of the script in the 'scripts' menu. This menu is automatically populated with the contents of the xfai_scripts folder on the computer indicated in the 'Remote server' field of the XFAI interface. A selected script can either be run by clicking the 'run' button, or edited, to show the second presentation of a script, as its textual source code in the 'source' pane of XFAI. By clicking on the 'Buttons' checkbox in the XFAI interface, you can see another presentation of a script. Buttons shows you GUI components of buttons, check boxes, menus and radio buttons that let you modify and run top-level calls in the script. The 'Buttons' view hides most of the details of the script and allows you to modify only a few parameters. It is great for demos and tweaking code without giving you the opportunity for creating a typo. Modifications made in this GUI interface are reflected back into the actual textual source so they get saved when the script is saved out to disk.

XFAI shows the results of a script in two ways. The first is a native Water printed representation of a Water object. The second is an HTML presentation similar to what a browser shows. Whatever can be displayed by a normal browser can also be displayed as the result of running a script. The switch between Water output and HTML-browser output happens automatically based on the returned value.

Each script may have an associated documentation file which can contain any HTML to describe the script to a human. XFAI automatically shows the documentation (if any) when a script is edited. In addition there is a link between XFAI and Traction for collaboration on a finer grained detail, allowing researchers to share comments about a given script. The capability to easily provide documentation, user comments, code, and the running of that code with multiple levels of running & modification across multiple computers AND coordinate all of this through a web browser interface, increases the productivity of researchers, their managers and early adopters of software innovations wherever the participants may be.