R-GMA User Guide for Python Programmers

1    I NTRODUCTION
1.1    P URPOSE AND S TRUCTURE OF THIS D OCUMENT
This document is intended to get people started with R-GMA. It is one of a set, with each member customised for a different programming language.

After this introduction there are sections explaining what should be done to ensure that R-GMA is correctly installed, how to publish information via a “Primary Producer”, how to get information back via a “Consumer”, how to set-up a “Secondary Producer” and how to use the command line and web based tools.

The APIs (in C, C++, Java and Python) are all described in detail in the documentation linked from http: //hepunx.rl.ac.uk/egee/jra1-uk/r-gma/ . In addition the documentation is all distributed with the software and may be found as $RGMA_HOME/share/doc/<module>/manual.pdf, where “module” identifies the document. Look at the directory $RGMA_HOME/share/doc to see the naming scheme.

Some brief release notes from a user’s perspective may be found in section 12 which is useful to anyone who is familiar with the previous version of R-GMA.

To understand more detail of what R-GMA is meant to do, you may choose to read the specification[1]. However we do not expect the average user to need the specification document.

This document contains a number of code examples. You can find a copy of these in the directory: $RGMA_HOME/share/doc/rgma-base/examples wherever R-GMA has been installed.

1.2    R-GMA A RCHITECTURE
1.2.1    V IRTUAL DATABASE
R-GMA is an implementation of the Grid Monitoring Architecture (GMA) proposed by the Global Grid Forum (GGF), which models the information infrastructure of a Grid as a set of Consumers (who request information), Producers (who provide information) and a single Registry (which mediates the communication between Producers and Consumers). R-GMA imposes a standard query language (a subset of SQL) on this model – so Producers publish tuples (database rows) with an SQL insert statement and Consumers query them using SQL select statements. R-GMA also ensures that all tuples carry a time-stamp, so that monitoring systems (which require time-sequenced data) are inherently supported.

R-GMA presents the information resources of a Virtual Organisation (VO)1 as a single virtual database containing a set of virtual tables. As the picture above shows, a single2 schema contains the name and structure (column names, types and settings) of each virtual table in the system. A single registry contains a list, for each table, of Producers who have offered to publish (provide data for) rows for the table. A Consumer runs an SQL query against a table, and the registry selects the best Producers to answer the query in a process called mediation. The Consumer then contacts each Producer directly, combines the information, and returns a set of tuples. The mediation process is hidden from the user. Note that there
is no central repository holding the contents of the virtual table; it is in this sense, that the database is virtual.

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