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Metadata Repository

On this page:

Motivation

Basics

It's optional

The repository being for a large site having hundreds or thousands of webs, its use is optional. It's activated only if the site owner explicitly turns on the metadata repository.

Structure

Examples

Here's how a metadata repository would be used by federated TWiki sites.

Federation of sites

Let's assume the following federation of TWiki sites.

site-mirroring.png

Web admins

If there are many webs, it may not be easy to get hold of people responsible for a web. So it's handy if all webs have their admins clearly defined. Given that, let's assume we define admins for each web and store as a part of web metadata.

Site metadata and web metadata fields

The following fields are needed in a site metadata record to implement the federation shown above.

And the site metadata table is as follows.
Name Server DataDir PubDir
am strawman /d/twiki/data /d/twiki/pub
eu woodenman /var/twiki/data /var/twiki/pub
as tinman /share/twiki/data /share/twiki/pub

And the following fields in the web metadata.

The web metadata table is as follows.
Name Admin Master
WebOne GodelGroup am
WebTwo EscherGroup eu
WebThree BachGroup as

How to get and put data - overview

Using these, you can construct a web interface to display and manipulate the webs table as follows.
Initial Letters:
Name Admin Master Load Row
 
WebOne GodelGroup am do
WebThree BachGroup as do
WebTwo EscherGroup eu do

mdrepo script from command line

Go to the bin directory then you can use the mdrepo script in the following format: ./mdrepo COMMAND ARGUMENT ... Arguments depend on the command.

mdrepo show TABLE RECORD_ID

Shows the specified record of the specified table.

Example:

$ ./mdrepo show sites am
am
    datadir=/d/twiki/data
    pubdir=/d/twiki/pub
    server=strawman

mdrepo list TABLE

Shows all the records of the specified table.

Example:

$ ./mdrepo list sites
am
    datadir=/d/twiki/data
    pubdir=/d/twiki/pub
    server=strawman

as
    datadir=/share/twiki/data
    pubdir=/share/twiki/pub
    server=tinman

eu
    datadir=/var/twiki/data
    pubdir=/var/twiki/pub
    server=woodenman

mdrepo add TABLE RECORD_ID FIELD_NAME=VALUE ...

Adds a new record. It returns nothing. If the specified record already exists, it complains.

Example:

$ ./mdrepo add webs WebFour admin=HofstadterGroup master=am 

mdrepo updt TABLE RECORD_ID FIELD_NAME=VALUE ...

Update an existing record. It returns nothing. If the specified record does not exist, it complains.

Example:

$ ./mdrepo updt webs WebFour admin=GardnerGroup master=am

mdrepo del TABLE RECORD_ID

Deletes an existing record. It returns nothing. If the specified record does not exist, it complains.

Example:

$ ./mdrepo del webs WebFour admin=GardnerGroup master=am

mdrep load TABLE FILE

Loads records to the specified table from the specified file. The file content is in the same format as the list command's output. Nonexistent records are created. Existing records are updated.

Example:

$ ./mdrepo load /var/tmp/temp-webs

mdrepo rset TABLE

Makes the specified table empty. It returns nothing.

Example:

$ ./mdrepo rset sites

mdrepo script from browser

Restrictions

Compared with command line use, browser use of mdrepo script is restricted for risk mitigation.

URL parameters

mdrepo script checks

The command is determined this way.

The table and the record ID are specified by the _table and _recid parameters.

Field values are specified by parameters of the =__FIELD_NAME format.

For example, submitting the following form has the same effect as the command line shown further below.

<form action="%SCRIPTURL%/mdrepo" method="post">
<input type="hidden" name="_add" value="add"/>
<input type="hidden" name="_table" value="webs"/>
<input type="hidden" name="_recid" value="WebFour"/>
<input type="hidden" name="__admin" value="GardnerGroup"/>
<input type="hidden" name="__master" value="am"/>
<input type="submit"/>

$ ./mdrepo add webs WebFour admin=GardnerGroup master=am

Output

By default, the script's output is in the text/plain MIME type. If the command succeeds, it returns nothing. When something goes wrong, an error message is returned.

If redirectto URL parameter is provided, the script returns HTTP redirect to the specified URL. If the redirectto parameter contains %RESULT%, it's replaced by the message to be shown when redirectto is not specified.

Configuration

To turn on the metadata repository, you need to have the following three settings.

$TWiki::cfg{Mdrepo}{Store} = 'DB_File';
$TWiki::cfg{Mdrepo}{Dir} = '/var/twiki/mdrepo';
$TWiki::cfg{Mdrepo}{Tables} = [qw(sites webs:b)];
$TWiki::cfg{Mdrepo}{Store}
Specifies a tie-able Perl class.
$TWiki::cfg{Mdrepo}{Dir}
Specifies a path to a directory where the MdrepoStore class have files.
$TWiki::cfg{Mdrepo}{Tables}
Specifies the names of the tables used. A table name may be followed by a colon and options. "b" is currently the only option recognized, which means the table can be updated from browser.

By the following setting, each web required to have its metadata record.

$TWiki::cfg{Mdrepo}{WebRecordRequired} = 1;
For a large site having thousands of webs, this is handy for site management. Specifically this brings the following behaviors.

Audit trail

When the mdrepo script is used either from command line or browser, if the command is either add, updt, del, or rset, it's recorded on the log file in the same manner as other scripts. Specifically, the activity is put on the 5th column.

Command 5th column format
add add TABLE RECORD_ID FIELD_NAME=VALUE ...
updt cur TABLE RECORD_ID FIELD_NAME=VALUE ...
updt TABLE RECORD_ID FIELD_NAME=VALUE ...
del cur TABLE RECORD_ID FIELD_NAME=VALUE ...
del TABLE RECORD_ID
rset cur TABLE RECORD_ID FIELD_NAME=VALUE ...
cur TABLE RECORD_ID FIELD_NAME=VALUE ...
...
rset TABLE
As the table above suggests, updt, del, and rset commands put multiple log entries so that the previous values are recorded. Here's an example of log entries left by a updt operation.
| 2012-06-15 - 13:16 | guest | mdrepo | TemporaryTestWeb.TestTopic | cur sites am datadir=/d/twiki/data pubdir=/d/twiki/pub server=strawman |  |
| 2012-06-15 - 13:16 | guest | mdrepo | TemporaryTestWeb.TestTopic | updt sites am datadir=/d/twiki/dat pubdir=/d/twiki/pu server=strawma |  |
When the mdrepo script is used from a command line, the topic name on the log is always Public.WebHome.

Audit trail is there by default. In case you want to suppress it, you can do it by setting a false value to $TWiki::cfg{Log}{mdrepo} configuration preference.

Only for top level webs

For practicality, web metadata is only for top level webs. More accurately, a subweb has the same web metadata as its parent.

The reason is that site administration gets complicated if subwebs can have different web metadata.

Related Topics: AdminDocumentationCategory, AutonomousWebs, ReadOnlyAndMirrorWebs, UsingMultipleDisks, UserMasquerading

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Revision: r1 - 2012-12-26 - 09:54:51 - TWikiContributor

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