One of the challenges of information systems is the accessibility of products residing in different remote servers and compose them to produce more complex information products. Problems in achieving this goal are related to legacy of different information systems that includes formats, applications, schemas, vocabulary, technologies.
Furthermore, the products in electronic form are becoming fairly complex, consisting of files (ASCII, XML, HTML, Word, etc.), interactive animations (e.g. Macromedia Flash), sound, video, images or embedded programs (e.g. Java applets).


Four tiers can be seen as a base of a distributed system:

The product tiers, formed by the servers containing the data; these could be in different formats, such as netCDF, HDF, ASCII, etc.
The product access and inventory tier, the access being provided by servers such as HTTP, and the inventory by catalog services.
The product catalog tier, allowing the selection of data.
The product presentation tier, that is
constituted by portals and must allow
different services, such as visualization.

In the case of harmonized components, the architecture to access products in a distributed system can be easily defined. But in general the architectures of data management systems residing in the different places have a high heterogeneity. A ‘transformation service’ is important in a system allowing access to data residing also in other data management systems, in order to transform queries and data between different logical scheme.

Different approaches can be adopted to access data residing in different servers, solutions are linked to the existence of (inter alia) common data policy, schema, vocabularies. The approach selected to built the information system that will be presented in this paper, is based on the idea to have a portal of portals, in which the heterogeneity is maintained. The main portal will contain all the information on metadata of products residing in the other portals, but property and download services will remain in the ‘product owner portal’. Vocabulary can be different (within certain limits) in the different portals, but the main will contain a trans-coding table.
Schema can be also different, it is only necessary to have access to particular final products. However, it is necessary to have a minimum common content in metadata, in order to allow queries by users. Format of metadata can be different, since it is transformed in central system. The disadvantage of a such approach is on the fact that the inclusion of new portals requires the implementation/adaptation of the ‘transformation’ software. The advantage is on the fact that the ownership of products remains in the original sites, and this does not create conflicts. Furthermore, the existing data management systems can be maintained. In operational sense, the ‘federation’ of different portals with their heterogeneity is effective since it assures the continuous update of portals content by local data managers, does not delay the response to queries, and assure the maximum profit both to data holders and users.

In this paper it is demonstrated that most of the problems to access products residing in different remote servers can be superseded in an effective way, using free software (PHP, MySQL, etc.) actually used in many information systems. The example is provided by the so called Mediterranean Operational Network (MOON) – Volunteer Observing Ship (VOS) Portal.

In September 1999, a Ship Of Opportunity Program was launched in the Mediterranean with the aim to provide data to the Mediterranean Forecasting System, i.e. the preoperational model forecasting the 3D circulation, temperature and salinity of the Mediterranean Sea. For this reason it was developed a portal for the access of data by users. During the last decade, the scope was enlarged in order to reach the need of a wider community of users: operational systems, climatic variability, research, public companies, students and the public. Furthermore, the portal has been implemented to access also products residing in remote servers. Actually access to products deriving from in situ and satellite data is offered to users.

The portal is providing the services defined in the INSPIRE directive: discovery, view, downloading, transformation. The implementation of the portal has been based on
specific rules on mission, quality and business:

Mission: definition of the general objectives; thematic information to be managed by the network; definition, implementation and maintenance of services;
Quality: quality assessment and QC procedures for data, products and services;
Business: specific data policy; pricing (if needed); ownership; use rules.

To facilitate the discovery service, a friendly user interface based on Google maps has been developed. This allow also to zoom on particular areas, maintaining the necessary geographical information.

In order to organize any information system, it is necessary inter alia to have additional definitions. In our case it is important to define ‘products’ and ‘services’:

  1. product is anything that can be offered to a client and that might satisfy a want or need (reference)
  2. service refers to a discretely defined set of technical functionalities