1.1.2. Service Design

Model-View-Controller

The service aspects of LBS mean that maps cannot generally be prepared in advance. They must be created at the moment they are needed. Producing maps in this way is termed ‘on-demand’ or ‘just-in-time’ mapping.

Service Components

In a location-based service, a provider allows user`s to access information resources, according to their interests and needs at a particular time and place. Information relevant to a user is then presented visually in ways that are adapted to suit the context of use. This description emphasizes three of the important aspects that need to be considered in an LBS design; the information itself (the map content), the interaction, and the visualization. Components realizing these aspects are commonly referred to as; the model, the controller, and the view.

Collectively these components can be described in relation to the model-view-controller (MVC) design pattern (Gamma et al.). MVC is used in almost all interactive computer systems, be they software products or Internet services. MVC will be used as a conceptual design model to organize the remaining units of this lesson.

Model

The model relates to the to the information sources that will be used to create an LBS map. It consists of the data itself as well as filters and functions that operate on the data. Because information sources are largely developed to suit a broad range of uses and situation, the model is the part of the service that is most similar to a product. The model includes:

Spatial data	Base maps, routes, and locations of places and objects of special interest, real-time data (e.g. traffic incidents)
Descriptive data	Descriptive text, photographs, video, and sounds related to the spatial data
Operations	Filter, search and update the information resource, perform processing on it (e.g. find the nearest, find the shortest route)

Controller

The functions of the controller are what makes the service heterogeneous and simultaneously produced and consumed. It interprets the user interactions with the device and the changes in their situation (e.g. location) and based on this specifies the contents that are relevant for display on the map. Essentially it provides the logic of the system. It includes:

Map Controls	Control map navigation (Zoom, Pan etc.)
Spatio-temporal Filters	Filter information according to the current location of the user and the time of use
Semantic Filters	Filter information according to themes relevant to the user's interests and activities(e.g. Italian restaurants)
Search	Allows the user to interactively look for descriptive and address based information

View

The view handles how the relevant information is presented to the user, e.g. graphically with a map or a text based or audio route description. It relates most closely to the intangible and perishable aspects of the service. The view includes:

Cartographic Display	Maps, Geographical descriptions e.g. routes
Textual Display	Web pages containing descriptive text and multimedia
Presentation rules	Map styling rules (e.g. which symbols to use for points-of-interest), style-sheets (e.g. for styling and laying out web pages)