Metacat

.. Note:: 

  Note that much of the functionality provided by the replication subsystem in Metacat

  has now been generalized and standardized by DataONE, so consider utilizing the

  DataONE services for replication as it is a more general and standardized approach

  than this Metacat-specific replication system.  The Metacat replication system

  will be supported for a while longer, but will likely be deprecated in a future

  release in favor of using the DataONE replication approach. 

technological, financial, and organizational sustainability approaches to 

process of writing scientific software both for servers and client tools.

DataONE acheives interoperability by defining a lightweight but powerful set of 

REST_ web services that can be implemented by various data management software 

systems to allow those systems to effectively communicate with one another, 

exchange data, metadata, and other scientific objects.  This `DataONE Service Interface`_

.. _REST: http://en.wikipedia.org/wiki/Representational_state_transfer

In DataONE, Member Nodes represent the core of the network, in that they represent

particular scientific communities, manage and preserve their data and metadata, and

provide tools to their community for contributing, managing, and accessing data.

DataONE provides a standard way for these individual repositories to interact, and helps

to coordinate among the Member Nodes in the federation.  This allows Member Nodes

to provide services to each other, such as replication of data for backup and failover.

To be a Member Node, a repository must implement the Member Node service interface, 

and then register with DataONE.  Metacat provides this implementation automatically,

and provides an easy configuration option to register a Metacat instance as a 

DataONE Member Node (see configuration section below). If you are deploying a Metacat

instance, it is relatively simple to become a Member Node, but keep in mind that 

DataONE is aiming for longevity and preservation, and so is selecting for nodes

that have long-term data preservation as part of their mission. 

The DataONE Coordinating Nodes provide a set of services to Member Nodes that

allow Member Nodes to easily interact with one another and to provide a unified

view of the whole DataONE Federation.  The main services provided by Coordinating

Nodes are:

* Global search index for all metadata and web portal for data discovery

* Resolution service to map unique identifiers to the Member Nodes that hold data

* Authentication against a shared set of accounts based on CILogon_ and InCommon_

* Replication management services to reliably replicate data according to 

  policies set by the Member Nodes

* Fixity checking to ensure that preserved objects remain valid

* Member Node registration and management

* Aggregated logging for data access across the whole federation

Three geographically distributed Coordinating Nodes replicate these coordinating 

services at UC Santa Barbara, the University of New Mexico, and the Oak Ridge Campus.

Coordinating Nodes are set up in a fully redundant manner, such that any of the coordinating

nodes can be offline and the others will continue to provide availability of the services

without interruption.  The DataONE services expose their services at::

  https://cn.dataone.org/cn

And the DataONE search portal is available at:

  https://cn.dataone.org/

.. _CILogon: http://www.cilogon.org

.. _InCommon: http://incommon.org

In order to provide scientists with convenient access to the data and metadata in

DataONE, the third component represents a library of software tools that have been 

adapted to work with DataONE via the service interface and can be used to

discover, manage, analyze, and visualize data in DataONE.  For example, DataONE

plans to release metadata editors (e.g., Morpho), data search tools (e.g., Mercury), 

data access tools (e.g., ONEDrive), and data analysis tools (e.g., R) that all 

know how to interact with DataONE Member Nodes and Coordinating Nodes.  Consequently,

scientists will be able to access data from any DataONE Member Node, such as a Metacat

node, directly from within the R environment.  In addition, software tools that 

are written to work with one Member Node should also work with others, thereby

greatly increasing the efficiency of creating an entire toolkit of software that

is useful to investigators.  

Because DataONE services are REST web services, software written in any

programming language can be adapted to interact with DataONE.

In addition, to ease the process of adapting tools to work with DataONE, libraries

are provided for common programming languages such as Java (d1-libclient-java) 

and Python (d1_libclient-python) are provided that allow simple function calls 

to be used to access any DataONE service.

Configuring Metacat as a Member Node

------------------------------------

Configuring Metacat as a DataONE Member Node is accomplished with the standard

Metacat Administrative configuration utility. To access the utility, visit the 

following URL::

  http://<yourhost.org>/<context>/admin

where ``<yourhost.org>`` represents the hostname of your webserver running metacat,

and ``<context>`` is the name of the web context in which Metacat was installed.

Once at the administrative utility, click on the DataONE configuration link, which

should show the following screen:

.. figure:: images/screenshots/screen-dataone-config.png

   :align: center

   The configuration screen for configuring Metacat as a DataONE node.

Being a replication target

~~~~~~~~~~~~~~~~~~~~~~~~~~

TODO: Describe the configuraiton for acting as a replication target.

Replication Policies

--------------------

TODO: Describe the replication policies for objects in DataONE.

Access Control Policies

-----------------------

TODO: Describe access control for objects in DataONE.

DataONE Configuration

~~~~~~~~~~~~~~~~~~~~~

Metacat can be configured to operate as a Member Node within the DataONE

federation of data repositories.  See :doc:`dataone` for background and details

on DataONE and details about configuring Metacat to act as a DataONE Member Node.

Replication Configuration

~~~~~~~~~~~~~~~~~~~~~~~~~

Metacat can be configured to replicate its metadata and/or data content to another

Metacat instance for backup and redundancy purposes, as well as to share data across

sites.  This feature has been used to create the Knowledge Network for Biocomplexity

(KNB), as well as other networks.  See :doc:`replication` for details on

the replication system and how to configure Metacat to replicate with another node.

.. Note:: 

  Note that much of the functionality provided by the replication subsystem in Metacat

  has now been generalized and standardized by DataONE, so consider utilizing the

  DataONE services for replication as it is a more general and standardized approach

  than this Metacat-specific replication system.  The Metacat replication system

  will be supported for a while longer, but will likely be deprecated in a future

  release in favor of using the DataONE replication approach.