Reuse and component design have extensively been applied to software engineering, but reuse and formal design methods in WWW-based system is still in its infancy. Most WWW developers currently design WWW content for the most efficient delivery and do not focus on these factors. This is because, at present, any extra code added to WWW components is often seen as non-essential. This resistance will be overcome over the next few years as the way that uses view content, and the way that they connect to the WWW changes. It is thus more likely that WWW pages will become more refined, and require much shorter design cycles than they typical have now. The key to this will thus be reuse, and in new application models which improved they way that content can be viewed, and reused. With the acceptance of XML (eXtensible Markup Language) as a standard modelling language, there will be an increase in the usage of formal model-ling languages, which integrate the WWW with the application domain. A good example of this is EML (Education Modelling Language), which tries to model the education process in a formal way, which can be easily interpreted within a WWW browser.
2 Components and Reuse
WWW pages are typically designed as single entities, and not really viewed as a collection of components. An enhanced way of designing WWW pages is to split the design into a number of interconnected components, each of which performs a specific task. For example most WWW pages have a layout which is constructed of a banner, a menu system, and a main content part (as illustrated in Figure 1). These can be constructed as reusable components which can be used to implement different design, using one or more of the following:
- Flash/XML. Macromedia Flash has supported XML for a while, and provides an excellent mechanism to produce reusable components, which are configured by XML. A distinct advantage with Flash is that the original design can be protected against copying. It also has the advantage over ASP/PHP as it does not need server-side processing.
A database can also be used to replace the XML definitions, but this adds a dependency on the underlying system. XML thus has the advantage that it can provide a platform independence to the WWW delivery.
The intercommunication of the components is important, but can cause problems with different browsers. A designer can thus use standard components which can be enhanced over time for layout, reliability, reconfigurability, and so on.
3 Application Modelling: An example
The WWW has evolved with a distinct lack of formal mod-els. This, of course, has allowed the WWW to quickly evolve, but has reduced the amount of reuse that can occur. This, though, is likely to change with the increased usage of formal modelling languages. A good example of this, in an education environment, is the EML. This language encapsu-lates the educational processes in a generic way including content design, delivery, and creation. An example of this type of language is one developed by the Open University of the Netherlands (OUNL) as a research project funded by the Dutch government. The system is based on XML and has now been released into the public domain. Their project aimed to create a comprehensive notational system that would enable the codification of courses, course components and programmes of study. For this, EML describes:
- All the content and logic of a learning unit - from resources such as texts and assessments.
- The roles and interactions of teachers and students.
- Any environmental facilities that may be required (such as progress tracking functions).
It thus specifies how different elements of an educational experience relate to one another, which provides a complete source from which the course can be interpreted and presented on to the user. This provides content creators with great flexibility when implementing a course as it adopts a pedagogical meta-model that provides a high-level abstrac-tion of learning methods. There is thus an interplay within EML-specified units of study, where actors (teachers and students) undertake roles within a learning environment. The objective here is to find 'a way to express any pedagogy at a sufficiently high level as to allow a diversity of approaches, while retaining usability'. EML thus has been designed to facilitate the creation of courses based on a wide range of educational philosophies.
The fundamental container within an EML-defined course is the unit of study, which specifies all the elements of learning activities and learning resources. Units of study can in themselves contain additional, nested units, allowing for the replication of complex and detailed course structures. The first level contains:
- Metadata. These are associated with a unit of study gives information about the course, such as statements of copyright and authorship.
- Objectives. These may be set to specify what students should have achieved upon completion.
- Prerequisites. These define what qualifications or abili-ties are expected of those starting to study.
On the next level we have:
- Content. This describes all the sources of learning mate-rial and activities employed.
- Method. This refers to the structure, methodology and processes inherent in a course.
In turn, these containers encompass:
- Roles. Specify the type of people to be involved in a course - that is, teachers, students and moderators.
- Activities. Define the activities to be undertaken by those fulfilling the different roles.
- Environment. These are objects that provide the neces-sary functionality for studying, such as communication facilities.
Figure 3 provides an overview of the structure of a unit of study, and though the concepts involved appear complex. As EML can define and develop e-learning materials, there are distinct advantages from an educational perspective in adopting it. In addition, OUNL supports the development of import and export filters to convert different data formats to and from EML. Furthermore, because modelling is text-based, it is possible for a number of people to work on different areas of a unit of study and for these elements, when complete, to be combined into a full course. Conversely, any element within the structure may be changed, removed, or replicated in another unit without difficulty. Indeed, customisation and reuse can be achieved simply by copying and pasting a block of notation between files. This must be contrasted with the complex operations of decompilation, collection and customisation required to reuse elements embedded in multime-dia software or web pages.
Another feature of the EML scheme is that developers need not consider the method of final delivery when designing courses. Units of study are accessed through player programmes which interpret EML and display the results within their own user interface and control system. Divorcing learning content and technical delivery considerations in this way has a number of advantages, such as when students find a particular user interface too complex or otherwise unsatisfac-tory they may, in theory, display the same course through a different player which is better suited to their needs. Also, as long as the same EML player is used between courses, each may share the same basic operating characteristics of that program. OUNL are developing an EML player called Edubox which is already being used in a number of different learning environments.
Figure 3: Relationship between elements in EML
There is a general focus on reuse of content on the WWW, and the forthcoming MPEG-21 standard  which will pro-vide an open standard for the delivery and consumption of multimedia. Essentially, it is an attempt to describe how the various elements within a multimedia experience relate to one another, and to create appropriate formats and specifications where gaps in the existing standards exist. As the initia-tive is described in the MPEG-21 overview document, '[t]he vision is to define a multimedia framework to enable transparent and augmented use of multimedia resources across a wide range of networks and devices used by different communities.'
There are seven key elements to the MPEG-21 standard:
- A uniform digital item declaration schema.
- A digital item identification and description framework.
- A uniform content handling and usage standard.
- An intellectual property management and protection sys-tem.
- A system for content representation.
- An event reporting and performance monitoring system.
The WWW is changing its form, which should allow for much greater reuse of
WWW content. The focus on this will be the increased acceptance
of standards such as XML, MPEG-21, and modeling languages, such
as EML. In the case of EML, the language encapsulates all the content
and logic of a unit of study, allowing for unprecedented reusability,
portability and customisation. The focus will thus be on creating
a solid model for content provision, and then creating differing
ways that the content can be presented.