Modelling hypermedia and web applications: the Ariadne Development Method

Abstract

The development process of hypermedia and web systems poses very specific problems that do not appear in other software applications, such as the need for mechanisms to model sophisticated navigational structures, interactive behaviors, interfaces with external applications, security constraints and multimedia compositions. Even though experience, modelling skills and abstractions can be borrowed from existing software design methods, such as object-oriented modelling, hypermedia developers need specific mechanisms to analyze and design using entities that belong to the hypermedia domain (such as nodes, links, anchors and space and time-based relationships). Moreover, hypermedia methods should provide mechanisms to deal with all the aforementioned features in a progressive and integrated way. In this paper, we present the Ariadne Development Method (ADM), a software engineering method that proposes a systematic, flexible, integrative and platform-independent process to specify and evaluate hypermedia and web applications. ADM has been shown particularly useful in complex systems involving a huge number of users with different abilities to access information, with a complex structure where a huge number of nodes have to be organized in a clear way to produce specifications that are discussed by people with an heterogeneous background. This is the case of ARCE, a Latin American project where 21 countries are cooperating to produce a web platform to improve assistance in disaster mitigation situations.

Introduction

The hypermedia paradigm relies on the idea of organizing information as a net of interrelated nodes that can be freely browsed by users selecting links and making use of other advanced navigation tools, such as indexes or maps. From the point of view of the application level, web sites can be considered as a subclass of hypermedia systems that use a specific technology to manage and deploy information but that share the same access philosophy. Throughout this paper we will use hypermedia as a generic term embracing all those applications that embed multimedia items in a hypertext structure, whether they are implemented using a web platform or not.

Hypermedia research has been addressed in different areas, including hypermedia construction, usability evaluation and metrics, navigation strategies or adaptive hypermedia. Significant efforts have been oriented toward applying software engineering methods that face up to the development of large and dynamic systems by applying a number of stages that give place to some products or artifacts. There is no doubt that software engineering methods are widely accepted in industrial as well as in academic environments in order to design software applications with a view to improve quality, reusability and maintenance. The experience gained in years of research in the software engineering field about modelling techniques, methods and methodologies can help to improve hypermedia development as suggested by Lowe and Webby [1]. In fact, most hypermedia methods use the notation of well-known data models, like the Entity-Relationship model [2] or OMT [3], in order to represent the system structure. However, these approaches cannot be used to model all the requirements of hypermedia systems since their development is much more incremental and iterative than in the rest of software systems [1] and, moreover, as Nanard and Nanard point out, software engineering lacks elements and mechanisms to model aesthetic and cognitive aspects which are a basic concern in hypermedia development [4].

In particular, the hypermedia development process poses rather specific problems that do not appear in other software disciplines [5], [6], such as the need for mechanisms to model: (1) sophisticated navigational structures, some of which can be ephemeral and adapted to the user needs; (2) interactive behaviors such as responses to specific events that occur or processes started when a specific status is achieved; (3) interfaces with external applications, such as databases; (4) multimedia compositions which have to be usable and aesthetic at the same time; and (5) security and access issues, which are becoming a key feature to be taken into account as most hypermedia applications, and particularly those implemented as web sites are often accessed by different users with different purposes, responsibilities [7], [8] and requirements.

Specific design mechanisms based on abstractions of the hypermedia domain (such as nodes, links, anchors and space and time-based relationships) are required to produce high-quality applications. Such hypermedia methods should provide mechanisms to deal with all the aforementioned features in a progressive and integrated way. In the last years several, methods for hypermedia design have been proposed, including RMM [9], OOHDM [10], [11], WSDM [12], WebML [13] and the OO-H method [14], but as demonstrated in [15] there are some modelling requirements that need still to be properly addressed.

In this paper, we introduce the Ariadne Development Method (ADM) that has two distinguishing features as a software engineering method: firstly, ADM considers six different design views: structure, navigation, presentation, behavior, processes and security, each of which is faced from different abstraction levels by means of a number of design artifacts; secondly, ADM proposes a systematic, flexible, integrative and platform-independent process to specify and evaluate hypermedia and web applications. Moreover, as a hypermedia-oriented method, four contributions of ADM can be highlighted:

• It offers a powerful mechanism to specify multimedia compositions which not only considers the definition of presentation features for multimedia items but also the specification of space and time-based relationships among information items. These relationships appear in most interactive systems, whether to settle constraints among the positions of certain objects (e.g., video a starts after video b) or to define system reactions (e.g., when the file icon overlaps the trash icon, the file icon disappears).

• It supports the modelling of functional requirements, so that not only navigation options and browsing semantics can be specified but also other complex services such as database access, information retrieval facilities or communication mechanisms.

• It supports user modelling. Users are most relevant component of interactive systems and they have to be analyzed to understand their requirements and preferences.

• It supports security and access policies specification. ADM assumes a high-level security model that makes possible to specify role-based access policies (RBAC) simpler and easier to maintain than group-based policies [7]. Such mechanism is used to specify both access and security rules, so that developers can determine which information and services are offered to each kind of user.

ADM has been shown particularly useful in the design and evaluation of complex systems involving a huge number of users with different abilities to access information, with a complex structure where multiple nodes have to be organized in a clear way to produce specifications that have to be discussed by people with an heterogeneous background (web programmers, stakeholders, graphical designers or content providers) and most of which are dynamically created. This is the case of the application example presented in this paper to illustrate the use of ADM: ARCE (“Aplicación en Red para Casos de Emergencia”). ARCE is a web system developed as a Latin American project where 21 countries are cooperating to produce a web-based platform to improve assistance in disaster mitigation situations [16]. According to the authors’ experience, ADM makes possible both to discipline developers, offering them a flexible but detailed development process to specify and evaluate all the hypermedia system features, and to involve stakeholders not only in the evaluation of prototypes but also in the assessment of conceptual models regarding system features such as navigation, presentation, structure, behavior, processes and security. ADM has little use in developing small hypermedia systems where no multimedia items are included and where no access rules are applied.

The rest of the paper is organized as follows. First some issues concerning hypermedia modelling are discussed in Section 2. Section 3 analyzes the most relevant features of ADM from two perspectives: as a software engineering method (Subsection 3.1) and as a hypermedia-oriented method (Subsection 3.2). Section 4 provides a detailed description of ADM and its application in a specific development project: ARCE. Section 5 is devoted to discussing the main ADM contributions compared to similar works and, finally, Section 6 summarizes some conclusions and ongoing works.