MODELLING LOCATION-AWARE BEHAVIOUR

IN WEB-GIS USING ASPECTS

Ana Oliveira

, Matias Urbieta

, João Araújo

, Armanda Rodrigues

Ana Moreira

, Sílvia Gordillo

and Gustavo Rossi

CITI/FCT Universidade Nova de Lisboa, Monte de Caparica, Portugal

Lifia, Facultad de Informatica, UNLP, Argentina

Keywords: Location-awareness, Aspect-oriented software development, Geographical information systems.

Abstract: Web-GIS applications evolve fast as new requirements emerge constantly. Some of these requirements,

particularly those related with spatial behaviours, might crosscut previous core application requirements.

Conventional modelling techniques, which ignore the effect of crosscutting concerns (such as tangling and

scattered behaviours) affect negatively the modularity and thus compromise application maintenance. In this

paper we present and aspect-oriented approach to model crosscutting concerns in Web-GIS applications,

particularly those related with spatial features. The process introduced in this paper starts with the

identification and specification of crosscutting concerns, followed by the composition of these concerns,

using the MATA language.

1 INTRODUCTION

Nowadays, web applications are more volatile than

ever due to new requirements that are either

requested by service providers or even by final

users. In particular Geographical Information

Systems (GIS) also has to deal with the requirements

volatility A reasonable way to deal with adding new

requirements into an application is to keep in

separate modules scattered behaviours by using

aspect-oriented techniques (Filman et al., 2005).

Our goal is to use aspect-orientation to deal with

GIS concerns in an oblivious fashion, modularizing

tangled and scattered behaviour, known as

crosscutting concerns. Concerns may be functional

or non-functional properties that represent needs of

the system. Crosscutting concerns are later

composed, or weaved, in different points, or

joinpoints, of the same or other applications. Typical

crosscutting concerns arise when dealing with

spatial data (e.g., user’s location) in Web Software.

Web-GIS applications tend to be complex as they

combine the volatile nature of Web software with

the inherent complexity of dealing with spatial data.

Location-aware behaviour, typical of Web-GIS,

usually cuts across other application concerns, since

it is likely to have an impact across different applica-

tion features (Munnelly et al, 2007).

Therefore, this paper introduces an aspect-

oriented approach to model common concerns in

Web-GIS applications, specifically those related

with spatial features. This approach is based on

aspect-orientation (Filman et al, 2005) and uses the

MATA language (Whittle and Jayaraman, 2007) to

specify aspects. We will demonstrate how spatial

behaviour can be isolated from other concerns to

improve modularity in our application domain.

The rest of the paper is structured as follows.

Section 2 presents a motivating example and

describes the background of our work. Section 3

introduces our approach for modelling GIS using a

running example. Section 7 presents related work.

Finally, Section 8 draws some conclusions and

describes future work.

2 CROSSCUTTING IN WEB GIS

A typical new requirement which may be added to a

Web GIS application is the “indoor representation”.

Figure 2 shows a web application for a shopping

centre that provides Indoor map support for

presenting store locations. The application offers a

“search function” to provide information about

416

Oliveira A., Urbieta M., Araújo J., Rodrigues A., Moreira A., Gordillo S. and Rossi G. (2009).

MODELLING LOCATION-AWARE BEHAVIOUR IN WEB-GIS USING ASPECTS.

In Proceedings of the 11th International Conference on Enterprise Information Systems - Information Systems Analysis and Speciﬁcation, pages

416-419

DOI: 10.5220/0002018604160419

 SciTePress

stores such as their address, their location inside the

shopping centre (Indoor position) – using the map

pointed with a dashed ellipse. This Figure also

shows an Outdoor map, which indicates the location

of the shopping centre in a global map. Both

examples (Figure 1 and Figure 2) reveal how the

same GIS requirements may be present in

applications of different nature, contemplating many

occurrences during one execution of the same

application.

The inclusion of this new requirement (indoor

representation) will create scattered and tangled

concerns in the application among its core or base

concerns. To make matters worse, adding other

concerns increases the application complexity

compromising its maintenance. (Section 5 describes

how to deal with these new requirements in more

detail).

Figure 1 illustrates how the introduction of new

requirements might impact in the application’s

structure. This Figure shows a UML sequence

diagram for “Show Store”, showing information

about a store. This is taken from the Web-GIS

application Maps@Web It contains tangled

behaviour as a consequence of composing several

GIS requirements such as Indoor Representation,

Location Sensing and Points of Interest. We can see

that the behaviour of each requirement is scattered

along the sequence diagram and crosscuts other

behaviour. For example, Location-aware crosscuts

Indoor and Outdoor representation, due to the

current user position that can be either in a global

map or into a specific building. Our goal is to

propose an approach for isolating and then

modelling these GIS concerns.

The concept of aspect was introduced by Aspect-

Oriented Programming (AOP) to modularize

concerns that could not be modularized using object-

orientation (Filman et al, 2005). Concerns may be

functional or non-functional properties that represent

needs of the system. In other words, a concern

comprises any coherent set of requirements, e.g., all

requirements referring to a particular functionality

(Baniassad et al, 2006). Crosscutting concerns are

concerns that cut across other concerns, creating

tangled and scattered representations of the program

that are difficult to understand and maintain (Rashid

et al, 2003). Aspect-Oriented Software Development

(AOSD) (Filman et al, 2005) appeared to handle

crosscutting concerns in all stages of the software

lifecycle. The MATA aspect-oriented modelling tool

is based on UML, allowing aspects composition

using class diagrams, sequence diagrams, etc.

To specify an aspectual scenario in MATA, three

stereotypes where created to define the composition

Figure 1: Sequence diagram with tangled behaviour due to

crosscutting concerns.

rules: <<create>> (states that the element will be

created in the base scenario), <<delete>> (states that

the element will be deleted of the base scenario),

<<context>> (states that the element will not be

affected by the other two stereotypes).Variables in

MATA are prefixed by a bar “|”, meaning that “|X”

will match to any class.

After specifying both kinds of scenarios, base

and aspectual, a pattern matching is made between

them. This means that the tool tries to establish a

connection between elements of each scenario,

always respecting the composition rules defined in

the aspectual scenario. The resulting composed

scenario describes, therefore, the behaviour of both

scenarios, according to the rules defined.

GIS applications are usually modelled using

simple approaches that are limited to the

identification of requirements and system functional-

ities, ignoring crosscutting concerns modularization,

as can be seen in (Longley et al, 2005).

The approach introduced in this paper aims at

improving the modularization of GIS Web

applications by modularizing typical GIS concerns.

The starting point is the identification and

specification of crosscutting concerns, which is

followed by the composition of the concerns

previously identified, using the MATA language.

3 MODELLING GIS CONCERNS

WITH ASPECTS

Figure 2 defines a process for modelling spatial con-

MODELLING LOCATION-AWARE BEHAVIOUR IN WEB-GIS USING ASPECTS

417

cerns using aspects in Web-GIS applications. The

process is divided into three main activities:

Identification, Specification and Composition.

Figure 2: Process for modelling GIS concerns with

aspects.

We will explain our approach using the GIS web

application Maps@Web, which is a Web application

providing a set of varied location-based services,

including services related with Cinemas, Hotels, or

Universities with the aim of helping users in their

daily activities. For instance, if the user wants to go

to the university and the cinema on the same

evening, this application will calculate an

appropriate path to access all these places.

To better demonstrate the contributions of our

approach, let’s add the new requirement “Indoor

Representation”. This requirement changes the

user’s application context, taking him to an indoor

representation of space. Next we show how to apply

the three activities of our approach.

Identification of Use Cases and Crosscutting

Relationships. This designs the use cases and

represents the relations among crosscutting use cases

using the stereotypes <<include>> and <<extend>>,

i.e., a use case that is included by several use cases

or a use case that extends several ones is considered

as crosscutting. In addition, we adopt a new

stereotype, <<trigger>>, to be used when a use case

activates one or more use cases. Figure 3 shows a

partial use case diagram, with the use case “Show

Service” and the crosscutting concerns “Change

Scale” and “Context Switch”. With the introduction

of the Indoor Representation requirement, we now

have two kinds of maps, Indoor Map and Outdoor

Map. In this example, when we want to see any

service, it starts with an outdoor representation of

the service location. That is why the use case “Show

Service” is connected with the concern “View

Outdoor Map”, with an <<include>> relationship.

This last concern will be extended with “Change

Scale” every time the map tool bar is changed.

When the scale reaches the maximum zoom

available, there will be a switch in the user’s

application context. We represent this relationship

between “Change Scale” and “Context Switch” with

an <<extend>> stereotype. When the scale reaches

the maximum and the context changes, the “View

Indoor Map” will be triggered.

Figure 3: Partial Use Case Diagram for Show Service; use

cases are enhanced with possible crosscutting concerns.

“Change Scale” and “Context Switch” are

crosscutting concerns and they crosscut other use

cases of the system (e.g. Edit Favourite Places,

Search by Service) not shown here due to space

limitations. They also interact with each other.

Use Case Refinement and Aspect Modelling. The

second activity of the approach specifies the base

scenarios (Figure 4) and the crosscutting concerns

with sequence diagrams (Figure 5 and 6). Figure 4

illustrates the “Show Suggestion” use case, chosen

by its importance to this example. Figure 5 shows

the crosscutting concern “Change Scale” represented

with the MATA sequence diagram. The first

message in this sequence diagram matches with the

same one in the base scenario. Figure 6 shows the

crosscutting concern “Context Switch” that will be

activated by the concern “Change Scale”. The first

message of the sequence diagram in Figure 6

matches with the equivalent one in the base scenario.

In this particular case, the base scenario is the aspect

“Change Scale”. This sequence diagram shows that

every time the user performs a change in the scale,

the system will verify if a change in the spatial

context is required. If this change is needed, the

system accesses the information about the new

context (in this case it is the indoor location). The

“any” fragment allows the base scenario to continue

its behaviour, with a sequence of messages.

Composition. It composes the aspectual scenarios

with the base scenarios using the MATA language.

The composition activity shows that the crosscutting

concerns can be isolated in aspects and then

composed into one or more base scenarios, without

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changing the application execution. By isolating the

crosscutting concerns, we promote modularization,

reuse, and evolution possibilities of the application.

Figure 4: Base Scenario "Show Suggestion".

Figure 5: Aspectual Scenario "Change Scale".

Figure 6: Aspectual Scenario "Context Switch".

4 RELATED WORK

The use of advanced separation of concerns

techniques and particularly the use of aspects have

been recently proposed for the development of

complex Web applications, mainly to provide

adaptation behaviours (Baumeister et al 2005).

Munnelly (Munnelly et al, 2007) presents an

approach for modularizing context-aware systems by

encapsulating different types of context using an

aspect-oriented approach. While Munnelly divides

the overall context space into eight sub-categories

and proposes an aspect-oriented approach for the

adaptation of the application to a specific context,

our approach presents a process for modelling

spatial concerns in a more abstract way.

In (Zipf and Merdes, 2003) the authors discuss

the use of aspects in GIS applications. However,

they only focus on the programming level, though

their analysis of spatial concerns is similar to ours.

5 CONCLUSIONS AND FUTURE

WORK

We have shown that in Web-GIS applications,

always in constant change, it is crucial to modularize

concerns to eliminate crosscutting of these concerns

in the application models. Our view represents a step

forward with respect to existing approaches in which

the spatial concerns are mixed with other

crosscutting application concerns.

Currently we are working on the identification

and modelling of more typical and recurrent GIS

concerns to obtain a catalogue which will let us get

new applications by composition following the style

shown in the paper. For the near future, we plan to

address crosscutting at the user interface level .

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