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To illustrate the possibilities of the XVergabe Bidder Interface, the following sections describe the exchange between bidder client and platform in some exemplary scenarios.

Subscribing for an open Tendering Procedure

The scenario in Figure 4 shows how a bidder client can subscribe a tendering procedure and download the tendering documents using the XVergabe Bidder Interface.

1. The bidder subscribes to an open tendering procedure he is interested in. The client calls the subscribe operation on the platform to make his interest known. The platform registers his subscription in its database.
2. The bidder synchronizes his local data with the platform’s data to become up to date. The client calls the getMessages operation to retrieve all messages directed at the client’s user. The list of messages returned contains a TenderMetaInformation and an InvitationToTender for the tendering procedure he previously subscribed for. The TenderMetaInformation message contains all the data about the procedure the client needs. The InvitationToTender message contains the IDs of the tendering documents among other information.
3. The client recognizes that the InvitationToTender message contains IDs of tendering documents and calls getDocument with these IDs to download the documents from the platform. After the download, the bidder can review the downloaded tendering documents.

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Figure 4 - Subscribing to a tendering procedure and downloading the tendering documents via XVergabe Bidder Interface.

Exchanging Questions & Answers

The scenario in Figure 5 shows how a bidder can send questions concerning a tendering procedure and receive the answers to the questions via the Bidder Interface.

1. The EO composes a set of questions (for example in the form of a PDF document) concerning a tendering procedure he previously subscribed for. These questions are sent to the platform by a call of sendMessage. The message is a ClientInquiry containing the questions document. The platform stores the questions document to be answered by the CA.
2. The contracting authority answers the questions and stores the answers in another document (again, this might be a PDF document) on the platform. Afterwards, the EO synchronizes his client to the platform. The client calls the getMessages operation and receives a ServerInquiry message (potentially among other messages). The ServerInquiry contains the ID of the answers document.
3. The client recognizes that the ServerInquiry contains the ID of a document and calls getDocument to download the document from the platform. The bidder can then review the answers.

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The XVergabe Bidder Interface defines a set of operations for end to end communication that are provided by a tendering platform and invoked by a bid client. Additionally, the interface defines a set of messages that can be exchanged between bidder client and platform with these operations.

Technically, the Bidder Interface is specified as a SOAP web service (see Figure 3). SOAP defines the protocol of the message exchange between bidder client and tendering platform. To define the structure of the exchanged messages, XSD (XML Schema Definition) is used. The exchanged messages themselves are represented in XML that meets the requirements of the XSD schema.

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Figure 3 - Technical implementation of the XVergabe Bidder Interface as SOAP web service.

The interface is implemented on both sides by solution providers: the bid client (active) and the tendering platform (passive). Communication between client and platform is always initiated by the client. The client uses one of the provided web service operations to send messages to the platform. The platform processes these messages and creates responses directed at the client. Since the communication is unidirectional, the client has to retrieve the messages directed at it, similar to using a mail client to retrieve mail from mail server.

Webservice Operations

The XVergabe Bidder Interface specifies five web service operations. Table 1 summarizes the function of each operation. The web service operations are specified in the file xvergabe-service.wsdl.

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