Concepts of VTQLserver

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The main idea is to create an interface to videotext so that different applications may access it. This is done with an server-client concept, where the server collects the pages and stores them in memory.

A client connects to a socket provided by the server. It sends VTQL commands to interact with the server and to access the pages database. All configuration of the server is also done within VTQL and may be changed at runtime without data loss.

Connection Modes

The server can provide different sockets for different modes of access. A socket is represented by a file and users with write access to the file may connect open a connection to the server. There are four modes of access:

In mode Nobody any connection will be closed immediately after showing some version info. In Event mode you get an output on every page the server has recieved, decoded and puted into the pages database; you may control the output by the event subset of VTQL commands. The Insert mode is for inserting pages by hand in the format PAGE ...HEX outputs. On any error the connection will be closed. The query subset of VTQL commands is available at the modes Query and Config. In these modes, you get a response to any input line, where the last line is "VOID", "SUCCESS" or "ERROR". In mode Config you may also use the configuraion subset of VTQL.

modeideacommand subset
Nobodyno access at allnone
Eventoutput every page if it gets stored to the database event
Queryallow any kind of query query
Configchange the configuration of the server query and configuration

Locking of Config Mode

It may be hard to configure the server, if you do not know whether some other connection does configuration in parallel. So you may lock your connection to disable the configuration subset of VTQL to any other connection. If you close your connection it will be unlocked automatically.

Stations

An important point of VTQLserver is, to store the pages per station: Pages are sent repeatedly, but you are only want to keep the latest version of a page. So, any page that matches the station match will be inserted into the the according station, replacing older pages with the same page and subpage number.

Page Timeout

Stations tend to reorganize their pages several times a day. So it may happen that the server holds pages, that belong to an older layout. This pages can be removed automtically by setting a page timeout for a station: A page gets removed from the pages database, if more then the specified number of pages has been recieved at this station.

Access to Video Device

In principle there is no need for an access to a video device and indeed, VTQserver works fine without it. There are three points, why it is usefull to let VTQLserver have access to it nevertheless: