The tourism sector was one of the first business sectors to take advantage of the possibilities of the Internet for the provision of tourism services. In this study there will be an attempt to approach and present the basic functions and architecture of a standard travel agency system on the Internet.

The Internet and Its Importance in the Tourism Sector

The tourism sector is one of the most important business sectors in Greece. One of the tourism service providers is the travel agency, which is also the main intermediary between the providers of basic tourism services and the final consumers. A travel agency, for example, is an intermediary agent acting on behalf of the client, making arrangements with tourism providers, airlines, hotels, travel guides, etc.

The term “online travel agency” refers to the transfer to the Internet of all or part of the tourism services offered by a real travel agency. The existence of a travel agency on the Internet does not necessarily imply the existence of a comprehensive and complete information system that will provide all the services that are available from the real agency. Many online travel agencies consist of a static website, which contains the name of the travel agency, its (actual) address and sometimes an e-mail address. The use of the Internet is for purely advertising purposes (Sugiyama et al., 2015). Although these travel agencies are not of particular interest, they are part of the above definition.

Of particular interest are the travel agencies offering even a small percentage of travel services over the Internet. There is an information system that is used to serve customers and tourists and provides search mechanisms for tourist information, booking services, etc. The mechanisms included by the majority of travel agencies in the information system, as well as the features and particularities that govern it are analyzed below (Bystrova et al., 2015):

- Nature of services offered by the travel agency. Some services, due to their form, cannot be transferred to the Internet completely automated, as there are limitations, such as the physical delivery of an air ticket.

- Know-how. Many times, although travel agencies can transfer their services on the Internet, they are unable to do so because of the lack of knowledge about the necessary technological infrastructure.

- Development costs. Travel agencies are unlikely to want to take such action, as there are factors like:

o The risk. It is not certain that such action will be successful.

o Insufficient information on the potential of the Internet. Many travel agencies do not know the real potential of the Internet.

- Maintenance costs. Many travel agencies do not have the financial capacity to develop and maintain a completely new, Internet-based travel services system,which will work alongside the existing one.

However, there are reasons that make this transfer attractive, even in the form of a simple presence of a travel agency on the Internet. Travel agencies consider that they will gain new customers through the Internet, and will be able to advertise their services to a huge, new mass of prospective customers (Xiang et al., 2015).

It is stressed that especially in the Internet a travel agency (like any other business) does not have to exist in its physical existence. There are many cases where a travel agency is established entirely in electronic form and serves its customers exclusively via the Internet.

3. Characteristics and Functions of an Online Travel Agency

The Basic Services of an Online Travel Agency

The services offered by travel agencies via the Internet vary. Typically, most travel agencies offer online services that can be fully automated (e.g. search services for tourist products). Of course there are some travel agencies that do not provide any online service. These support their existence on the Internet for purely advertising purposes (Roger-Monzó et al., 2015). The tourist services currently offered by the various travel agencies are grouped into three categories (Table 1):

- Tourist information search services

- Booking services

- System management services

Table 1. Basic services of an online travel agency

Search servicesBooking servicesSystem management servicesSearch for tourist products:

- Travel packages

- Hotels

- Means of transport

- Cruises

- Tickets (air, boat, etc.)Booking of tourist products through:

- Special booking forms (online or in a conventional way)

- Direct communication with the travel agency via e-mail.These services are optional and concern the travel agency:

- Online introduction of tourist information

- Updates

- Collection of statistics

- Immediate customer service with automated notification

on the course of their booking information etc.

Source: Xiang, Magnini and Fesenmaier, 2015

In their majority, existing travel agencies on the Internet offer both tourist search services and booking services. But few are the travel agencies that offer dynamic search or online booking services.

Technological developments and the needs of the consumers (fast and correct service, direct search results) impose the use of the newest application development techniques (use of a database for the dynamic extraction of information, the ability to make a booking online, etc.)

For a fuller understanding of the functions of an online travel agency, it is necessary to examine the actors involved in all phases of operation. In order to make a trip through an online travel agency, the involvement of three actors is necessary (Lin, 2016):

- Providers of basic tourist services

- Customers

- Intermediaries (travel agencies)

This categorization requires the creation of three different subsystems that will serve the needs of each actor. The role of these actors is the same as the role they play in their offline commercial transactions. The provider of basic tourist products and services sells and promotes its products to the customer/consumer. The customers are looking for the products they want and then, if they want, they buy them. The intermediaries, i.e. the travel agency, are those that undertake to bridge the gap between the providers and the final customers. An analysis of the services offered is presented in the following for each subsystem.

3.2. The Customer Subsystem

It is the main subsystem, because it is the part of the tourist application that the interested customer sees. More specifically, the possibilities that an online travel agency can offer to the customer are:

Electronic directory services: The most basic service to be offered to the user is the description of the tourist products and services through the websites of the travel agency. Their simple reading is a service that replaces the traditional way of reading tourist directories (Swann et al., 2016).

Search services: This service includes the search for a tourist package, the search for cruises, the search for hotels, etc. The search for tourist products can take place through many different ways:

- Search criteria: The search criteria that can be used vary. The search criteria can be the price of the tourist product, departure and booking dates, country of destination, etc. A typical example is the 4U2 Travel Agency (http // www.focusmn.com/4u2/welcome.html).

- Navigation engines: such as through a geographic map (e.g. the Cruise Web - www.cruiseweb.com)

- A list of tourist products by category (e.g. Travel Plan, http://www.travelplan.gr)

In any case, the search takes place on the database of the tourist system and the data that meets the criteria set by the user is dynamically derived. The database is a prerequisite for the proper operation of a travel agency and for the best possible provision of service to its clients.

Booking services: Booking of tourist products can be made via online booking mechanisms. The user just enters all the details required for the booking by simply filling in an online form. For security reasons, this service must allow the user to enter his/her username and personal password. In this way, the system assumes the automatic certification of the data. In some cases there is the possibility of immediate payment (using electronic payment technologies). Many tourist systems, however, provide bookings only by e-mail (Buhalis and Amaranggana, 2015).

Communication services between users and a travel agency. It is the only service that all the ideal travel agencies offer to their users. Thus, users can e-mail comments, make reservations for tourist products (if online booking is not available), answer questionnaires designed to improve the system by the travel agency, etc.

Provision of additional services: such as making use of the possibilities offered by multimedia. The users are now able to see directly on their computer screens, images or videos from the destination they are interested in visiting or the hotel they are interested in booking a room. In this way, the users obtain an initial picture of the tourist product they are interested in, a feature that is not available in the traditional ways of searching and booking.

The Provider Subsystem

It is the main subsystem for entering data into the travel agency’s database. The principal responsible for the introduction and reliability of the data is the provider himself, who is interested in promoting his/her tourism products through the proposed system. In the case of travel agencies, the agency itself usually plays the role of the provider. However, there are cases, as already mentioned, in which a travel agency does not have a physical presence, but has been created only for the Internet. These travel agencies are called Virtual Travel Agencies. In this case, the role of the provider is assumed either by other travel agencies with which the virtual agency has a contract, or directly by hotels, airlines, shipping companies, etc. More specifically, an online travel agency may offer on behalf of the provider:

Online import of tourist products: This service must include the introduction of the features of the tourist packages, the hotel information, the details of the air or ferry ticket, etc. (Page, 2014). The input of the data from the provider is the basic prerequisite for the proper operation of the proposed system.

Tourist products search services: In the case of a virtual travel agency, safety measures must be taken between different providers (usernames and passwords).

Tourist products information services: The provider has the ability to modify or delete one of the features of a tourist product offered. For example, they can change the price of a tourist package (due to reduced interest), delete it if it is no longer offered, or add new packages, etc. (Benur and Bramwell, 2015).

Booking and customer tracking services: The provider can monitor the booked reservations and obtain information for the customers.

The Intermediary Subsystem

It is the management subsystem of the entire tourist information system. More specifically, an online travel agency should provide the following management guidelines:

Provider Subsystem Services: Services for the online introduction, deletion, modification, etc. of tourist products should be offered, similar to those of the provider, so that the travel agency itself can manage the tourist products it offers (Vaughn et al., 2015).

Customer management services: The services of this type are very important because in this way the travel agency can monitor the transactions made by its clients and draw useful conclusions from them. By monitoring, for example, customers' preferences regarding the places they prefer to visit may increase the supply of the tourist packages with the highest demand.

But more interesting are the benefits that a travel agency can gain by transferring the provision of its services to the Internet. The intermediary actor/travel agency can benefit from such an action as it can offer several additional services: