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xFeed AJAX data publication documentation

Abstract: The xFeed example application of the xsdb package provides an infrastructure which makes it easy to implement "type ahead suggest" drop down selections matching against large or small data sets. The xFeed example illustrates how the xsdb framework can simplify data management and transmission in real applications. All software described here is open source and freely available for use and modification by anyone. This document explains how to install and use xFeed.

Keywords: AJAX, Asyncronous Javascript with XML, data publication, database, xsdb, Python, data feed, open source, web development, active pages.

Audience: This document is intended for internet professionals who would like to add AJAX type ahead suggestion functionality to documents on their web sites. Readers may use the software described here directly or use the information provided here supplimented with the source code to help them develop their own AJAX functionality.

Prerequisites: To understand this document you need to have a basic familiarity with HTML and Javascript. To implement the techniques described in this document you must be able to add web pages to an internet server. To add the optional indexing methods described below you must be able to add Python CGI scripts or Apache web server mod-python components to an internet server. This software uses recent Javascript features and may not work properly in combination with older browsers (see comments below).


AJAX (asynchronous javascript with XML) is a web methodology which provides advanced highly usable interfaces in web pages. AJAX technology uses features of XML, javascript, HTML, and server side software.

One of the most common applications of AJAX is "type ahead suggestions" where an AJAX component combines some of the information typed into a web form with information provided from a web server in order to suggest likely completions for elements of the web form. This document discusses the xFeed package which provides a simple methodology for implementing type ahead suggestions. Some live demos of pages that use the methodology are the xFeedMe zipcode demo page (which uses btree indexing on the server) and the xFeedMe state information page (which uses a static xsdb data page).

For example the page shown below provides information on books and prices. In the screen-shot the user has typed the book title prefix "apoc" and the AJAX interface has automatically determined the full names of all books that start with that prefix. (This interface shown is available live on the internet at

EXAMPLE: When the user types the prefix "apoc" the xFeed form watcher offers suggested completions.
In this example the user may select any of one the options in the drop down box to fill in the complete book name and all of the other data fields about that book automatically.

The xFeed package implements this kind of functionality as follows:

EXAMPLE: When the user types the prefix "apoc" for the title and "v" for the author the rest of the form values are filled with the information for the only matching book.

This document shows the steps required to create an xFeed enabled page with auto-completion functionality, which requires the following general steps.

Publish the xsdball.js and formWatcher.js java script modules on
Provide some sort of server component which publishes xsdb formatted data in response to HTTP queries.
Create and publish an HTML page including a web form and a javascript onload function which initializes and starts a FormWatcher for that form, connecting it to the xsdb server data source.
Please note that because of the "SAME SOURCE" javascript security restriction all components must be installed on the same server ( Also, it should be mentioned that step (B) can be very simple or very complex. This document will discuss steps A and C and will describe three ways to implement step B.

STEP A: Publishing javascript components

In order to use the xFeed component you must publish the xFeed and xsdb javascript components on your server. These components run on the client browser and not on your server -- but the server must provide them to the client as text.

Get the xFeed distribution (from, the downloads page of the xsdb sourceforge distribution) and unzip it. The two required files are

I publish these files on my servers by placing them at
(The simple way to do this is to copy the xsdbXML directory under the SERVERROOT.)

This makes the files available to clients at the URLs
If you put the files in some other server relative location you must make appropriate changes to URLs mentioned in this document to reflect the location you chose.

STEP B option 1: Using a static xsdb source file

One of the reasons xFeed is easy to use is that it does not necessarily require any "live" server component in order to work -- for small data sets or for testing purposes you may use a static xsdb data file to provide the server information required by the form. The javascript xsdb implementation is capable of evaluating any xsdb query using static data without any help from the server.

This approach is only advisable for testing and small data sets because for larger data sets the extra processing required by the client (in the same processor thread as the graphical interface) makes the browser user interface slow and jerky.

For example we may publish a file containing information about U.S. States provided in the distribution as

By placing the file under the server root at
This makes it possible for clients to load the contents of the file
<title>State names, trees, flowers and capitals of U.S states</title>
  <s at="State">alabama</s>
  <s at="Capital">montgomery</s>
  <s at="StateTree">longleaf pine</s>
  <s at="TreeScientific">pinus palustis</s>
  <s at="StateFlower">camelia</s>
  <s at="FlowerScientific">camellia japonica</s>
  <s at="State">alaska</s>
  <s at="Capital">juneau</s>
using the URL
An xFeed enabled web page can extract appropriate data from this file automatically. You can test that the data is available by opening the URL for the xsdb page (the browser will probably try to interpret the page as html, so it will look strange, but if you "view source" you should see the xsdb data).

Note that all values in the xsdb file content such as alaska are in lower case letters. For simplicity at this writing the FormWatcher component only works with lower case letters. Please complain if you need it to handle mixed case also. Until this limitation is lifted please make sure that any static xsdb data files used with a FormWatcher has only lower cased values.

STEP C: Creating an xFeed enabled form

An xFeed enabled web page will usually include three components: The StatesSimple.html example page has these components in the following general outline:
<script language="JavaScript">
// the form watcher must be bound to a global variable
var Watcher = null;

// this function is called after the page is loaded (body.onload())
function OnLoadFunction() {

<body onload="OnLoadFunction()">

<form name="StateForm" id="StateForm">

<script src="/xsdbXML/xsdbjs/xsdball.js">
<script src="/xsdbXML/xFeed/formWatcher.js">

The contents of the form and the OnLoadFunction have been deferred and the required xsdb components "/xsdbXML/xsdbjs/xsdball.js" and "/xsdbXML/xFeed/formWatcher.js" are put at the end of the HTML text to allow the browser to format the HTML before the javascript files are loaded.

The form includes a number of input elements that the FormWatcher will attempt to automatically complete.

<form name="StateForm" id="StateForm">
<input type="reset" value="reset"><br>
State Name: <input type="text" name="State" size="40"> <br>
State Capital: <input type="text" name="Capital" size="40"> <br>
State Tree: <input type="text" name="StateTree" size="40"> <br>
State Tree (scientic name): <input type="text" name="TreeScientific" size="40"> <br>
State Flower: <input type="text" name="StateFlower" size="40"> <br>
State Flower (scientific name): <input type="text" name="FlowerScientific" size="40">
In this case for simplicity the names of the input elements match the attribute names for the data values in the xsdb source file. Thus the input element named Capital
  <input type="text" name="Capital" size="40"> <br>
is to be associated with the xsdb values associated with the name Capitol like
  <s at="Capital">juneau</s>
The form id (with value StateForm) is also important because the FormWatcher uses the id to locate the form.

The OnLoadFunction() initializes the FormWatcher and specifies the form elements to complete

// the form watcher must be bound to a global variable
var Watcher = null;

// this function is called after the page is loaded (body.onload())
function OnLoadFunction() {
	// create a watcher and bind autofill attributes to form input elements
	Watcher = new FormWatcher("Watcher", "StateForm", "states.xsdb", 55);
	// since the data is static, preload and compile it
	// identify the input elements to watch
	//start watching;
Note that we must declare a global variable (in this case named Watcher) to house the form Watcher at the global javascript scope.

The constructor

	Watcher = new FormWatcher("Watcher", "StateForm", "/test/states.xsdb", 55);
creates a FormWatcher associated with the form with the id StateForm and bound to the xsdb data source at relative URL /test/states.xsdb (which resolves to the absolute URL The 55 specifies that no drop down completion box should have more than 55 elements.

The directive

should only be used with static data sources such as /test/states.xsdb. The preload directive preloads the data file text and "precompiles" it to reduce network traffic and unneeded reprocessing.

The directive

directs the Watcher object to attempt autocompletions for the State input element of the StateForm form listed above.
	<input type="text" name="State" size="40">
By default the input element name is assumed to be the same as the data attribute name. The full calling sequence for Watcher.complete
	Watcher.complete(id, noDropDown, bindAttribute)
binds the form element id to the attribute name bindAttribute and if noDropDown is true the watcher will not generate drop down completions for that element (which may be desired if it sometimes contains long values).

Finally the function starts the watcher main loop;
in this case specifying that the watcher should check the form for changes every 2000 milliseconds (every 2 seconds). This starts a "polling loop" where the watcher repeatedly This loop continues so long as the page is active. (The actual implementation is more complex than the outline above.)

And that's all you need (for small data). No special server side software required. You should be able to open the HTML page (, type yu into the State Flower input element, and in a couple seconds all appropriate values for "new mexico" (with state flower "yucca") should be filled in automatically.

If it doesn't work you could try:

Unfortunately you will probably find that as the static data size grows larger the query interface will become jerky and you will want to do more processing at the server, which will require installing some sort of server side component which responds to xsdb queries.

STEP B option 2: Using a CGI script in Python with BTree indexing to respond to xsdb queries

The xFeed package comes with an example server component for replying to xsdb queries posed by a client such as the FormWatcher. This component indexes table files provided as tab delimited text (as explained below) and serves xsdb formatted replies to queries using the indices. Programmers can use this approach directly or implement other approaches using this one as an example if desired. The example is configured for use either using CGI scripts or using mod-python under Apache. This section discusses the CGI script methodology. You may need to modify some or all of the absolute paths mentioned below to reflect your configuration.

Prerequisites: To use the Python CGI script you must have Python installed with a web server configured to support CGI scripts. You also must install the xsdb python implementation as discussed in the xsdb Python documentation.

In my case I have Apache installed on my Win32 workstation with CGI scripts enabled for scripts in the directory C:\Apache\Apache\cgi-bin which appears as the server relative directory My xsdb and xFeed distributions are placed under C:\xsdbSourceForge\.

Get the data. The xFeed indexer supports source data provided in tabbed delimited text format with a header line. An example of this format is provided in the distribution at xsdb/xsdbXML/xFeed/testdata/ containing information about books and book prices. If you open this large file in a text editor such as emacs or WordPad it looks like this:

ISBN	TitleAsShown	Subtitle	TitlePageNames	Abstract	...
9004108157	The Missionary Lives	A Study in Canadian Missionary Biography 	...
9004079270	Medieval Islamic Symbolism and the Paintings in the ...
Here many rows and columns have been omitted. The first line provides attribute names for each column (each separated by a single tab character), and subsequent lines provide values for each column (separated by single tabs). Each line is terminated with a new line character. This is a very common format supported by many programs such as MySQL, Access, Excel, to name three.

Prepare the index. Preprocessed indices allow the xFeed cgi script to find records of interest more quickly than it could by scanning the entire file for every access. The following simple python script distributed as xsdb/xsdbXML/xFeed/testdata/ builds indices using data from

import sys
sys.path.append("..") # make sure MatchAssertion module can be found
import MatchAssertion

M = MatchAssertion.TreeMatcher("bookprices")
f = open("")
indexAttributes = ["ISBN", "TitleAsShown", "Subtitle",
                   'AuthorsList', 'MainCategory', 'SubCategory']
M.CreateFromDataLinesWithHeader(f, indexAttributes, verbose=True)
When run in the directory xsdb/xsdbXML/xFeed/testdata/ opens the file as f and constructs indices for each of the attribute names in the list
	indexAttributes = ["ISBN", "TitleAsShown", "Subtitle",
                   'AuthorsList', 'MainCategory', 'SubCategory']
in the index files bookprices_0.idx through bookprices_5.idx. These B-tree based indices are now available for use by the CGI script which feeds xsdb data to the FormWatcher client.

The cgi script (provided in the distribution as xsdb/xsdbXML/xFeed/testdata/BookFeed.cgi) makes use of the bFeed.Feeder object which effectively hides most of the steps required to implement a CGI script.

import sys
mydir = r"C:\xsdbSourceForge\xsdbXML\xFeed"
sys.path.append(mydir) # make sure the bFeed module can be found
import bFeed

f = bFeed.Feeder(mydir+"/testdata/bookprices")
Here the first group of statements identify the script as a Python script (to be executed by c:\python23\python.exe) and make sure that the Python system path includes the directory containing the bFeed module before importing that module. The statement
	f = bFeed.Feeder(mydir+"/testdata/bookprices")
constructs a Feeder object f associated with the index files created above and the line
executes the CGI processing to handle a request. In particular the doCGI method The actual processing is more complex than this, but the above lists the general idea.

To enable this CGI script move BookFeed.cgi to a cgi-bin directory for your server (in my case to C:\Apache\Apache\cgi-bin. In some cases you may need to do other things like make the cgi-script file executable (see your server documentation) and modify the absolute paths listed in the file content.

Test the cgi script. At this point if all went well you should be able to test your cgi-script by pointing a browser at<s%20at="ISBN">9004106219</s>
or a similar URL reflecting your configuration. This access requests that BookFeed.cgi find a match to the query <s at="ISBN">9004106219</s>. In my case the CGI script works and the browser presents the following XML.
Now the BookFeed.cgi CGI script is ready to be used by a FormWatcher on an HTML page. The distribution provides xsdb/xsdbXML/xFeed/testdata/CGISimple.html as a simplified example page which uses BookFeed.cgi to update a form. This HTML file is very similar to the StatesSimple.html example given above.

The form in CGISimple.html is similar to the form for StatesSimple.html except that it has a different id, different form elements and some of the form elements are sometimes large enough that they must be presented using a textarea input element.

<form name="BookForm" id="BookForm">
<input type="reset" value="reset"><br>

ISBN: <input type="text" name="ISBN" size="13"> <br>
Title As Shown: <input type="text" name="TitleAsShown" size="40"> <br>
Subtitle: <input type="text" name="Subtitle" size="40"> <br>
list of authors: <input type="text" name="AuthorsList" size="40"> <br>
Main Category: <input type="text" name="MainCategory" size="40"> <br>
Subcategory: <input type="text" name="SubCategory" size="40"> <br>
abstract: <textarea name="Abstract" cols="40" rows="8"></textarea> <br>
short abstract: <textarea name="ShortAbstract" cols="40" rows="3"></textarea> <br>
Readership: <textarea name="Readership" cols="40" rows="3"></textarea> <br>
Reviews: <textarea name="Reviews" cols="40" rows="3"></textarea> <br>
Author CV: <textarea name="CV" cols="40" rows="3"></textarea> <br>
phase of publication: <input type="text" name="Phase" size="20"> <br>
number of pages: <input type="text" name="NumberOfPages" size="13"> <br>
Cover info: <input type="text" name="Cover" size="13"> <br>
List price (euros): <input type="text" name="ListPriceEuro" size="13"> <br>
List price (dollars): <input type="text" name="ListPriceDollar" size="13"> <br>
Publication Date: <input type="text" name="PublicationDate" size="13"> <br>
Series Title: <input type="text" name="SeriesTitle" size="40"> <br>
Volume Number: <input type="text" name="VolumeNumber" size="13"> <br>


The onload function for the CGISimple.html is similar to the onload function for StatesSimple.html except that the watcher is bound to the correct form name BookForm, the correct data source /cgi-bin/BookFeed.cgi and the data is not preloaded.

// the form watcher must be bound to a global variable
var Watcher = null;

// this function is called after the page is loaded (body.onload())
function onLoadFunction() {
	// create a watcher and bind autofill attributes to form input elements
	Watcher = new FormWatcher("Watcher", "BookForm", "/cgi-bin/BookFeed.cgi", 20);
	// also bind attributes that will not have drop down completions
	Watcher.complete("Abstract", true);
	Watcher.complete("ShortAbstract", true);
	Watcher.complete("Readership", true);
	Watcher.complete("Reviews", true);
	Watcher.complete("CV", true);
	Watcher.complete("Phase", true);
	Watcher.complete("NumberOfPages", true);
	Watcher.complete("Cover", true);
	Watcher.complete("ListPriceEuro", true);
	Watcher.complete("ListPriceDollar", true);
	Watcher.complete("PublicationDate", true);
	Watcher.complete("SeriesTitle", true);
	Watcher.complete("VolumeNumber", true);
	//start watching;
Also, since many of the attributes are not appropriate for drop down list box completion suggestions the Watcher is bound to them with NoDropDown set true, for example as in
	Watcher.complete("ShortAbstract", true);
Finally the Watcher polling loop is started with the polling interval set to 1000 milliseconds (1 second).

To enable CGISimple.html for your server move it to an appropriate location under your server root, perhaps under htdocs/test so it corresponds to the URL If everything is hooked up properly you should now be able to point a browser at, type gods into the "list of authors" input box and see the Watcher automatically fill in all values corresponding to the book with ISBN 9004129553.

STEP B option 3: Using Apache mod_python with BTree indexing to respond to xsdb queries

If you happen to be running an Apache web server with the mod-python component available you can get a further performance enhancement by using a mod-python module in place of a CGI script. The mod-python implementation improves on the CGI implementation since it does not need to reinitialize the Python interpreter and reopen the index files for every access. This section is briefer than the others because mod-python is less common than CGI scripting and if you know how to use it you are probably pretty savvy and don't need many hints :).

The mod-python option is almost identical to the CGI option except that the mod-python module code (provided in the distribution as xsdb/xsdbXML/xFeed/testdata/ looks something like this

import sys
mydir = "/home/awatters/webapps/mod_python/htdocs/xsdbXML/xFeed"
import bFeed

f = bFeed.Feeder(mydir+"/testdata/bookprices")

def BookFeed(req, q, at=None):
    result = f.doModPythonPublisher(req, q, at)
    return result
Here again the bFeed.Feeder abstraction hides most of the mechanisms needed for the implementation. Another difference is that the URL for the mod-python module differs from the URL for the CGI script. In my case the server relative URL becomes /xsdbXML/xFeed/ Consequently the HTML page which uses the mod-python book feed must be bound to the new url as
	Watcher = new FormWatcher("Watcher", "BookForm", "/xsdbXML/xFeed/", 20);
In all other particulars the mod-python option is similar to the CGI option.

Additional comments

This is early release software. I think I've seen situation where the Watcher polling loop quits for mysterious reasons. The suite seems to work with recent browsers including MSIE 6, Firefox 1.5, and Safari 2.0. Your mileage may very.

A number of features of the package are not documented here. Please look to the source if you want to find more options.

For the moment all strings are translated to lower case for simplicity. A relatively simple elaboration (involving shadowing cased values with lowercased copies) would get around this issue, but it has not been implemented at this writing.

There are a lot of possible ways xFeed could be extended. Please offer suggestions to Aaron Watters ( (me).


End of xFeed AJAX data publication documentation
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