.. _sec-intro:

Introduction
************

The :term:`GDS` is a modular expandable dissemination and publication server. The
**purposes of GDS** are:

1. Automatic and manual dissemination of information about earthquake, tsunamis
   and others
#. Provision of information as bulletins, figures showing maps, waveforms or diagrams,
   or externally provided files such as reports in PDF format
#. :ref:`Filtering<sec-intro-proc>` of the supplied information based on earthquake
   parameters such as location or magnitude and the subscribed recipients
#. Dissemination using :ref:`many services<sec-into-diss>` which can be customized
#. Flexible format customization of the disseminated information including
   multi-language support
#. Fast manual dissemination by efficient template selection based on configurable
   pull-down selection menus and interactive parameter input.

GDS uses a plugin technology to import earthquake solutions from different
sources, filter the incoming earthquake information and disseminate template
based messages through various communication channels such as SMS, email, fax
and web. :term:`GDS` complements the functionality of :term:`SeisComP` in the
domain of dissemination of notifications and warnings.

Figure :num:`fig-intro-arch` shows :term:`GDS` architecture. It is composed
of a bunch of individual modules which acquire (gray), process (green) and
disseminate (blue) earthquake information. In addition a web interface (red)
exists which allows to configure, interact and review the dissemination process.

.. _fig-intro-arch:

.. figure:: media/architecture.*
   :width: 16cm

   Architecture of GDS


.. _sec-into-acqui:

Acquisition
===========

gempa GmbH developed a new protocol to exchange earthquake information in real-time or time
window based with :term:`QuakeLink`,
an appendant software module. The :term:`QuakeLink` server is the central acquisition component.
It offers import plugins to get earthquake information from different
sources such as a :term:`SeisComP` system. The :term:`GDS` back-end and the web
interface connects to the :term:`QuakeLink` server listening for new earthquake
information or to query historic events.

.. _sec-intro-proc:

Processing
==========

The :ref:`sec-be` connects to :term:`QuakeLink` to receive earthquake
updates. Based on configured criteria new earthquake information is filtered for
matching subscriptions. Subsequently subscription specific bulletins are created
with the help of configurable templates. These bulletins are stored in spool
directories accompanied by an address list.

For the configuration of the processing step a web interface is provided which
operates on a database provided by the :term:`GDS` back-end. In addition the
web interface directly connects to the back-end to allow the user to manually
control the dissemination process. This includes (re-)triggering the
dissemination of events as well as reviewing and editing of bulletins prior to
dissemination. The list of available earthquakes for dissemination is fetched
from the :term:`QuakeLink` server.

.. _sec-into-diss:

Dissemination
=============

Almost any service, e.g., email, SMS, fax, Twitter, TV, web, and many more, can
be used to disseminate the information.  For each service a separate spool
directory is used. :term:`Spooler` applications monitor these directories and
send the data to the various recipients. The advantages of decoupling the
:ref:`sec-be` from the actually dissemination work are:

* **Reliability** - If one dissemination channel resp. :term:`Spooler` is
  blocked it will not interfere with other channel.
* **Flexibility** - A :term:`Spooler` may be stopped, reconfigured or even
  exchanged without any affect on the :ref:`sec-be`. Also custom :term:`Spooler`
  may be coded in any possible programming language since the data is exchanged
  via plain files.
* **Reusability** - Often dissemination tools working with files already exist
  and may be used right away without or with very little modification.

For convenience reasons :term:`Spooler` applications may be added to the
:ref:`sec-be` configuration which will cause them to be started as sub processes.

New version in 2019
===================

A totally new version of GDS is provided as of mid 2019. The new features include:

#. A totally :ref:`updated web interface<sec-web>` for controlling the dissemination and log review
#. Enhanced support for manual dissemination based on pre-configured content templates
#. New filter and spooler options, e.g.

   * add distance and direction to the nearest and other city to bulletins
   * add examples for generating shake maps using `SIGMA <https://www.gempa.de/products/sigma/>`_

#. Event selection by Flinn-Engdahl region

Read the :ref:`CHANGELOG<sec-changelog>` of GDS for a complete list.