WebExp2 Experimenter's Manual - School of Informatics - University ...

• comments can be written like this:
• attribute values must always be quoted
A fuller description of XML and the precise rules that govern its use can be found in the excellent tutorial at
http://www.w3schools.com/xml
4.2.2 Reading XML
As every property or object must be defined within these matching opening and closing tags, XML results in
a rather verbose experimental description. However it is straightforwardly legible with a little practise, and
particularly with indentation and a code-colouring text editor which will show you the distinction between your
property tags and their values.
An excellent and versatile editor which will colour XML for you is Scite, available for free from http://www.
scintilla.org.
Using XML also means that it is simple to validate and transform both experimental designs and results, and
makes it relatively legible to a non-technical user.
4.3 How to write an experiment in XML
To implement an experiment you must write an XML file describing the sequence of the experiment, and
optionally one or more resource files which describe your stimuli. An experiment is described by a Timeline
which consists of one or more Stages, each of which contains one or more Slides. The Timeline therefore is
the root element of the XML document. The next section describes the function and behaviour of the elements
(stages, slides, components) which you define within the timeline.
Observing the XML ‘well-formedness’ rules (section 4.2.1), you define your stages and slides along with their
properties; filling the slides with components, which act as stimuli and collect responses for you. Then you can
run the experiment, and your sequence of slides gets displayed.
If you describe an unknown or inapplicable property within your XML, it will be ignored during the experiment.
However the document must be a ‘well-formed’ XML document. Some information is output to the logs about
illegal properties and values, so you can clear up anything that may be providing unexpected behaviour.
Note: In 2005/6 we should be developing a front-end for WebExp2 which will simplify the process of designing
slides, shielding the user from the repetitive task of defining the XML by hand.
4.4 Description of the Slide
The slide is the area where you display the components (stimuli and responses) that you want to present in
each step of your experiment. Think of it as a point in the sequence of your experiment, and as the page where
you will present the stimulus to the subject, whether that is a picture, some text, an audio clip, or an animated
image; and where you will also present components for collecting responses and input.
Components are arranged on the screen by defining a layout for your slide, specifying row and column sizes
and positioning components within the resulting grid. You can specify the visual properties of font and color
when describing a slide, which will provide defaults for any visual components you place onto the slide.
Each slide is used to present stimuli to the subject. These stimuli can be defined within the slide description,
but it is more sensible to separate the changeable content of your experiment from the form. You can do this
by writing separate files which describe your stimulus resources, and importing these into your slides. This is
described in a later section.
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