Glossary

From SRB

Contents 1 Glossary of Technical Terms 1.1 Sample Session: 1.2 Querying Examples: 1.2.1 Find all values of latitudes in the sensor schema 1.2.2 Find all rows in sensor table 1.2.3 Find all rows in sensor table for wind related sensor_types 1.2.4 Find all rows in sensor table and the related data in SRB for wind related sensor_types 1.2.5 Do the above for non-wind related data 1.2.6 For non-wind-related sensors find their validity periods 1.2.7 Repeat the same with data_name 1.2.8 Find all sensors that are running 1.2.9 Repeat the above query but restricting to wind-related sensors 1.2.10 Find all authors associated with a SRB file 1.2.11 Dind the same with sensor name information 1.2.12 Rerun above query with validity information also 1.3 Modifying and inserting new values into these extensible tables. 1.3.1 Inserting New Data into a Table (need to know table name use Squery with -L to find this) 1.3.2 Updating the Values in a Row 1.3.3 Deleting a Row in a Table 1.4 Details of schema and table values used in example

Glossary of Technical Terms

Collection 

A collection is a logical name given to a set of data objects. All data objects stored in SRB/MCAT are stored in some collection. A collection can have sub-collections, and hence provides a hierarchical structure. As a simple analogy, a collection in SRB/MCAT can be equated to a directory in a Unix file system. But unlike a file system, a collection is not limited to a single device (or partition). A collection is logical but the data objects grouped under a collection can be stored in heterogeneous storage devices. There is one obvious restriction, the name given to a data object in a collection or sub-collection should be unique in that collection.

Compound Resource 

A compound resource allows the SRB to function as a complete (although basic) archival storage system (also known as an hierarchical storage system (HSM)). A compound resource may be configured to contain a pool of cache resources and a tape resource. When a user creates a file using a compound resource, the object created becomes a "compound object". The actual data of a "compound object" may reside on cache or tape or both. Unlike the SRB replica, a "compound object" always appears as a single object even though there may be multiple copies of the data. It is a simple hierarchical system where data migrate automatically between cache and tape. Data is always staged on cache automatically whenever it is accessed and migrates to tape by the system administrator when more cache space is needed. The cache and tape resources can be distributed across a WAN.

Container 

A Container is a way to put together a lot of small files into one larger file to improve performance. This works very well with resources that include tapes (such as HPSS). The whole container is retrieved from tape, cached on SRB disk, and then multiple files can be quickly read and written on the container copy on disk. The SRB handles the book-keeping for the container. Also see the FAQ container items.

Data object 

A data object can usually be thought of as a file, although it can also be a real-time data stream, or database binary large object. Also see the FAQ item

DataSet 

This term is equivalent to Data object (not a Collection).

Dublin Core 

The Dublin Core is a metadata element set. It includes all DCMI terms (that is, refinements, encoding schemes, and controlled vocabulary terms) intended to facilitate discovery of resources. See Dublin Core.

Extensible Metadata 

==How to use the extended schema capabilities of SRB.==

SRB uses the MCAT metacatalog to store metadata about various entities in SRB. This includes metadata about users, resources, data, collections, containers and zones. Apart from the core-metadata (pre-defined schema) maintained for these entities, the MCAT also has multiple ways of storing additional metadata in an extensible fashion.

There are two ways to provide this extensibility for an SRB system.

1. The first one, familiarly, is through the user-defined metadata table which allows a user to add attribute-value-unit type metadata to data, collections, resources as well as users.
2. The second way provides an easy way to extend the core by allowing users to add tables to MCAT instance and access them through the native SRB/MCAT interfaces.

In this document we discuss the second method. The first method is discussed in the man page for Sufmeta.

In this case we provide a means for a user/SRB admin to expose new tables that are not in the core MCAT but are located in the same schema/instance as the MCAT or accessible from the schema. Currently we do not provide creation of these tables through the SRB (for security purposes) but this restriction will probably be relaxed in a later release.

There are three actions needed to be done for the MCAT to provide the access to the extensible tables.

1. Providing a logical schema-name and attribute-name for the table and is attributes. This information is provided by populating the table MDAS_TD_EXTAB_INFO in the core schema.
2. Providing the referential relationship with other extensible tables and/or MCAT core tables. This information is provided by adding one-line per referential link in the metadata.fkrel.ext file in the data directory.
3. Adding a new srbObject (any size file will do) in the /home/ext_schema/table_names collection with the table name as the object name. Write/All access to these files translates to modify/insert/delete access to the tables.

The table MDAS_TD_EXTAB_INFO is in the core schema and has the following attributes:

           Name                                    Type
-----------------------------------------  ----------------------------
         EXT_SCHEMA_NAME                           VARCHAR2(250)
         EXT_TABLE_NAME                            VARCHAR2(250)
         EXT_ATTR_NAME                             VARCHAR2(250)
         EXT_ATTR_OUT_NAME                         VARCHAR2(250)
         EXT_ATTR_COMMENTS                         VARCHAR2(250)
 

The EXT_SCHEMA_NAME and the EXT_ATTR_OUT_NAME name are the information that is exposed to the user.

For example there might be the following rows in the schema table:

   EXT_SCHEMA_NAME  EXT_TABLE_NAME  EXT_ATTR_NAME  EXT_ATTR_OUT_NAME  EXT_ATTR_COMMENTS
   ---------------  --------------  -------------  -----------------  -----------------
   roadnet          srb.sensor      sensor_name    sensor_name        sensor name of data stream
   roadnet          srb.sensor      sensor_type    sensor_type        sensor type of data stream
   roadnet          srb.sensor      location_lat   latitude           sensor latitude
   roadnet          srb.sensor      location_lon   longitude          sensor longitude
   roadnet          srb.sensor      data_id                           FK to SRB data_id
   roadnet          srb.validity    start_date     start_date         start of a valid period
   roadnet          srb.validity    end_date       end_date           end of valid period
   roadnet          srb.validity    comments       v_comments         validity comments
   roadnet          srb.validity    sensor_name                       FK to srb.sensor.sensor_name
   mets             sekar.m_core    data_name      object_name        name of object in METS
   mets             sekar.m_core    author         creator            name of creator of METS objects  
   mets             sekar.m_core    data_id                           FK to SRB data_id

The metadata.fkrel.ext file should have the following to show the relationships for the above rows:

srb.MDAS_ADC_REPL data_id srb.sensor data_id A

srb.MDAS_ADC_REPL data_id sekar.m_core data_id A

srb.sensor sensor_name srb.validity sensor_name A

The new objects created are:

orion-803% Sput -S  orion-sekar-ufs  metaFile /home/ext_schema/table_names/srb.sensor

orion-804% Sput -S  orion-sekar-ufs  metaFile /home/ext_schema/table_names/srb.validity

orion-805% Sput -S  orion-sekar-ufs  metaFile /home/ext_schema/table_names/sekar.m_core

(the above operation creates one file per table)

orion-807% Sls -l /home/ext_schema/table_names
/home/ext_schema/table_names:
  sekar       0 orion-sekar-ufs              105 2005-03-31-09.58 % sekar.m_core
  sekar       0 orion-sekar-ufs              105 2005-03-31-10.00 % srb.sensor
  sekar       0 orion-sekar-ufs              105 2005-03-31-09.58 % srb.validity

orion-808% Schmod w public npaci /home/ext_schema/table_names/srb.sensor

orion-809% Schmod w public npaci /home/ext_schema/table_names/srb.validity
 
orion-810% Schmod w public npaci /home/ext_schema/table_names/sekar.m_core

(the above operations provide write access control to these files which translate to write access to these files. Currently read access is not controlled )

The first two lines shows the relationship to the MCAT core schema and the last line between the two tables in the sensor schema.sensor_name

One can then query across mets, roadnet and core schema using the Squery (see man pages). The schema attributes can be listed using H,E or U options of the Squery command.

Sample Session:

orion-131% Squery -H -L |head
0:DATA_ID -> MDAS_AD_REPL.data_id
1:DATA_REPL_ENUM -> MDAS_ADC_REPL.repl_enum
2:DATA_NAME -> MDAS_AD_REPL.data_name
 :
 :
397:EXTENSIBLE_ATTR_NAME -> MDAS_TD_EXTAB_INFO.ext_attr_name
398:EXTENSIBLE_ATTR_OUTSIDE_NAME -> MDAS_TD_EXTAB_INFO.ext_attr_out_name
399:EXTENSIBLE_ATTR_COMMENTS -> MDAS_TD_EXTAB_INFO.ext_attr_comments

orion-134% Squery -E -L
420:mets.creator -> sekar.m_core.author
421:mets.data_id -> sekar.m_core.data_id
422:mets.object_name -> sekar.m_core.data_name
423:roadnet.data_id -> srb.sensor.data_id
424:roadnet.location_lat -> srb.sensor.location_lat
425:roadnet.location_lon -> srb.sensor.location_lon
426:roadnet.sensor_name -> srb.sensor.sensor_name
427:roadnet.sensor_type -> srb.sensor.sensor_type
428:roadnet.v_comments -> srb.validity.comments
429:roadnet.end_date -> srb.validity.end_date
430:roadnet.sensor_name -> srb.validity.sensor_name
431:roadnet.start_date -> srb.validity.start_date

Querying Examples:

Find all values of latitudes in the sensor schema

orion-139%  Squery -S roadnet.location_lat
--------------------------- RESULTS ------------------------------
location_lat: 10N
-----------------------------------------------------------------
location_lat: 20.3N
-----------------------------------------------------------------

Find all rows in sensor table

orion-140%  Squery -S roadnet.location_lat -S roadnet.location_lon -S roadnet.sensor_name -S roadnet.sensor_type
--------------------------- RESULTS ------------------------------
location_lat: 10N
location_lon: 50W
sensor_name: SCA
sensor_type: wind North in meters per second
-----------------------------------------------------------------
location_lat: 10N
location_lon: 50W
sensor_name: SCB
sensor_type: wind East  in meters per second
-----------------------------------------------------------------
location_lat: 20.3N
location_lon: 40W
sensor_name: AFS
sensor_type: temp in deg c
-----------------------------------------------------------------
location_lat: 20.3N
location_lon: 40W
sensor_name: AFU
sensor_type: time in GMT
-----------------------------------------------------------------

Find all rows in sensor table for wind related sensor_types

orion-145% Squery -S roadnet.location_lat -S roadnet.location_lon -S roadnet.sensor_name 
	-S roadnet.sensor_type roadnet.sensor_type like '*wind*' j=427:srb.sensor:sensor_type:roadnet.sensor_type
--------------------------- RESULTS ------------------------------
location_lat: 10N
location_lon: 50W
sensor_name: SCA
sensor_type: wind North in meters per second
-----------------------------------------------------------------
location_lat: 10N
location_lon: 50W
sensor_name: SCB
sensor_type: wind East  in meters per second

Find all rows in sensor table and the related data in SRB for wind related sensor_types

orion-155% Squery -S DATA_NAME -S roadnet.location_lat -S roadnet.location_lon -S roadnet.sensor_name 
	-S roadnet.sensor_type roadnet.sensor_type like '*wind*'
--------------------------- RESULTS ------------------------------
data_name: Spwd2.c
location_lat: 10N
location_lon: 50W
sensor_name: SCA
sensor_type: wind North in meters per second
-----------------------------------------------------------------
data_name: Spwd2.c
location_lat: 10N
location_lon: 50W
sensor_name: SCB
sensor_type: wind East  in meters per second
-----------------------------------------------------------------

Do the above for non-wind related data

orion-156% Squery -S DATA_NAME -S roadnet.location_lat -S roadnet.location_lon 
	-S roadnet.sensor_name -S roadnet.sensor_type roadnet.sensor_type 'not like' '*wind*'
--------------------------- RESULTS ------------------------------
data_name: Spwd.c
location_lat: 20.3N
location_lon: 40W
sensor_name: AFS
sensor_type: temp in deg c
-----------------------------------------------------------------
data_name: Spwd.c
location_lat: 20.3N
location_lon: 40W
sensor_name: AFU
sensor_type: time in GMT
-----------------------------------------------------------------

For non-wind-related sensors find their validity periods

orion-167% Squery  -S roadnet.sensor_name -S roadnet.start_date 
	-S roadnet.end_date roadnet.sensor_type  'not like' '*wind*'
--------------------------- RESULTS ------------------------------
sensor_name: AFS
end_date: 2004-08-18-04.40
start_date: 2004-02-10-10.30
-----------------------------------------------------------------
sensor_name: AFS
end_date: 2005-01-10-02.20
start_date: 2004-08-20-11:12
-----------------------------------------------------------------
sensor_name: AFS
end_date: 2999-12-31-12.00
start_date: 2005-01-11-01.43
-----------------------------------------------------------------
sensor_name: AFU
end_date: 2004-08-15-2.22
start_date: 2004-02-10-10.30
-----------------------------------------------------------------
sensor_name: AFU
end_date: 2005-01-10-02.20
start_date: 2004-08-20-11:12
-----------------------------------------------------------------
sensor_name: AFU
end_date: 2999-12-31-12.00
start_date: 2005-01-11-01.43
-----------------------------------------------------------------

Repeat the same with data_name

orion-168% Squery -S DATA_NAME  -S roadnet.sensor_name -S roadnet.start_date 
	-S roadnet.end_date roadnet.sensor_type 'not like' '*wind*'
--------------------------- RESULTS ------------------------------
data_name: Spwd.c
sensor_name: AFS
end_date: 2004-08-18-04.40
start_date: 2004-02-10-10.30
-----------------------------------------------------------------
data_name: Spwd.c
sensor_name: AFS
end_date: 2005-01-10-02.20
start_date: 2004-08-20-11:12
-----------------------------------------------------------------
data_name: Spwd.c
sensor_name: AFS
end_date: 2999-12-31-12.00
start_date: 2005-01-11-01.43
-----------------------------------------------------------------
data_name: Spwd.c
sensor_name: AFU
end_date: 2004-08-15-2.22
start_date: 2004-02-10-10.30
-----------------------------------------------------------------
data_name: Spwd.c
sensor_name: AFU
end_date: 2005-01-10-02.20
start_date: 2004-08-20-11:12
-----------------------------------------------------------------
data_name: Spwd.c
sensor_name: AFU
end_date: 2999-12-31-12.00
start_date: 2005-01-11-01.43
-----------------------------------------------------------------

Find all sensors that are running

orion-169%  Squery -S roadnet.sensor_name -S roadnet.start_date roadnet.v_comments '=' running  
--------------------------- RESULTS ------------------------------
sensor_name: AFS
start_date: 2005-01-11-01.43
-----------------------------------------------------------------
sensor_name: AFU
start_date: 2005-01-11-01.43
-----------------------------------------------------------------
sensor_name: SCA
start_date: 2004-10-21-10:20
-----------------------------------------------------------------
sensor_name: SCB
start_date: 2004-10-21-10:20
-----------------------------------------------------------------

Repeat the above query but restricting to wind-related sensors

orion-170%  Squery  -S roadnet.sensor_name 
	-S roadnet.start_date roadnet.v_comments '=' running roadnet.sensor_type like  '*wind*'
--------------------------- RESULTS ------------------------------
sensor_name: SCA
start_date: 2004-10-21-10:20
-----------------------------------------------------------------
sensor_name: SCB
start_date: 2004-10-21-10:20
-----------------------------------------------------------------

Find all authors associated with a SRB file

orion-172% Squery -S DATA_NAME  -S roadnet.sensor_name 
--------------------------- RESULTS ------------------------------
data_name: Spwd.c
sensor_name: AFS
-----------------------------------------------------------------
data_name: Spwd.c
sensor_name: AFU
-----------------------------------------------------------------
data_name: Spwd2.c
sensor_name: SCA
-----------------------------------------------------------------
data_name: Spwd2.c
sensor_name: SCB
-----------------------------------------------------------------

Dind the same with sensor name information

orion-173% Squery -S DATA_NAME  -S roadnet.sensor_name -S mets.creator
--------------------------- RESULTS ------------------------------
data_name: Spwd.c
author: Frank Vernon
sensor_name: AFS
-----------------------------------------------------------------
data_name: Spwd.c
author: Frank Vernon
sensor_name: AFU
-----------------------------------------------------------------
data_name: Spwd.c
author: Kent Linquist
sensor_name: AFS
-----------------------------------------------------------------
data_name: Spwd.c
author: Kent Linquist
sensor_name: AFU
-----------------------------------------------------------------
data_name: Spwd2.c
author: Frank Vernon
sensor_name: SCA
-----------------------------------------------------------------
data_name: Spwd2.c
author: Frank Vernon
sensor_name: SCB
-----------------------------------------------------------------
data_name: Spwd2.c
author: Kent Linquist
sensor_name: SCA
-----------------------------------------------------------------
data_name: Spwd2.c
author: Kent Linquist
sensor_name: SCB
-----------------------------------------------------------------

Rerun above query with validity information also

orion-174% Squery -S DATA_NAME -S roadnet.sensor_name -S mets.creator -S roadnet.start_date 
	-S roadnet.end_date -S roadnet.v_comments 
	
--------------------------- RESULTS ------------------------------
data_name: Spwd.c
author: Frank Vernon
sensor_name: AFS
comments: power shut down
end_date: 2004-08-18-04.40
start_date: 2004-02-10-10.30
-----------------------------------------------------------------
data_name: Spwd.c
author: Frank Vernon
sensor_name: AFS
comments: running
end_date: 2999-12-31-12.00
start_date: 2005-01-11-01.43
-----------------------------------------------------------------
data_name: Spwd.c
author: Frank Vernon
sensor_name: AFS
comments: sensor calibration
end_date: 2005-01-10-02.20
start_date: 2004-08-20-11:12
-----------------------------------------------------------------
:
:
-----------------------------------------------------------------
data_name: Spwd.c
author: Frank Vernon
sensor_name: AFS
comments: sensor calibration
end_date: 2005-01-10-02.20
start_date: 2004-08-20-11:12
-----------------------------------------------------------------

---

Modifying and inserting new values into these extensible tables.

These are done through the SmodE Scommand. These functionalities require the user to know both the internal table name and the attribute names in the table which are possibly different from the schema-name and external attribute names which are logical mappings.

Inserting New Data into a Table (need to know table name use Squery with -L to find this)

orion-230% SmodE -i Spwd.c /home/sekar.sdsc/mytest srb.sensor 'DATA_ID|SENSOR_NAME|SENSOR_TYPE|LOCATION_LAT|LOCATION_LON'  
	"0|'LAB'|'Seismic sensor with Z value'|'20N'|'38W'"

Attribute names DATA_ID, USER_ID, TIME_VAL and COLLECTION_ID are keywords and will be substituted if 0 is used as the default value.

orion-233% Squery -S roadnet.location_lat -S roadnet.location_lon -S roadnet.sensor_name 
	-S roadnet.sensor_type roadnet.sensor_type like '*Seismic*'
--------------------------- RESULTS ------------------------------
location_lat: 20N
location_lon: 38W
sensor_name: LAB
sensor_type: Seismic sensor with Z value
-----------------------------------------------------------------

orion-249% SmodE -i Spwd.c /home/sekar.sdsc/mytest srb.validity 'sensor_name|start_date|end_date|comments'
	"'SCA'|'2004-02-10-10.30'|'2004-02-22-10.20'|'internal software error'"

orion-253% Squery -S roadnet.sensor_name -S roadnet.start_date -S roadnet.end_date -S roadnet.v_comments roadnet.sensor_name = 'SCA'
--------------------------- RESULTS ------------------------------
sensor_name: SCA
comments: internal software error
end_date: 2004-02-22-10.20
start_date: 2004-02-10-10.30
-----------------------------------------------------------------
sensor_name: SCA
comments: running
end_date: 2999-12-31-12.00
start_date: 2004-10-21-10:20
-----------------------------------------------------------------

Updating the Values in a Row

orion-235% SmodE -u Spwd.c /home/sekar.sdsc/mytest srb.sensor  SENSOR_TYPE "'seismic sensor with Z value'" SENSOR_NAME "= 'LAB'"

orion-236% Squery -S roadnet.location_lat -S roadnet.location_lon -S roadnet.sensor_name -S roadnet.sensor_type roadnet.sensor_name = 'LAB'
--------------------------- RESULTS ------------------------------
location_lat: 20N
location_lon: 38W
sensor_name: LAB
sensor_type: seismic sensor with Z value
-----------------------------------------------------------------

Deleting a Row in a Table

orion-239% SmodE -d Spwd.c /home/sekar.sdsc/mytest srb.sensor SENSOR_NAME "= 'LAB'"
orion-240% Squery -S roadnet.location_lat -S roadnet.location_lon -S roadnet.sensor_name -S roadnet.sensor_type roadnet.sensor_name = 'LAB'
No Answer found for the Query
Squery Error: -3005
orion-241% Squery -S roadnet.location_lat -S roadnet.location_lon -S roadnet.sensor_name -S roadnet.sensor_type
--------------------------- RESULTS ------------------------------
location_lat: 10N
location_lon: 50W
sensor_name: SCA
sensor_type: wind North in meters per second
-----------------------------------------------------------------
location_lat: 10N
location_lon: 50W
sensor_name: SCB
sensor_type: wind East  in meters per second
-----------------------------------------------------------------
location_lat: 20.3N
location_lon: 40W
sensor_name: AFS
sensor_type: temp in deg c
-----------------------------------------------------------------
location_lat: 20.3N
location_lon: 40W
sensor_name: AFU
sensor_type: time in GMT
-----------------------------------------------------------------

Details of schema and table values used in example

create table sensor 
 (
  data_id  number(38),
  sensor_name   varchar(250),
  sensor_type   varchar(250),
  location_lat  varchar(250),
  location_lon   varchar(250)
 );
create table validity
 (
  sensor_name   varchar(250),
  start_date    varchar(32),
  end_date      varchar(32)
 );
create table m_core
 (
  data_id  number(38),
  author   varchar(250),
  data_name varchar(250)
 );


srb.sensor
 DATA_ID   SENSOR_NAME SENSOR_TYPE                        LOCN_LAT    LOCN_LON
--------------------------------------------------------------------------------------
 35332292  AFS         temp in deg c                      20.3N       40W
 35332292  AFU         time in GMT                        20.3N       40W
 35332293  SCB         wind East  in meters per second    10N         50W
 35332293  SCA         wind North in meters per second    10N         50W


srb.validity
 SENSOR_NAME   START_DATE            END_DATE            COMMENTS
-----------------------------------------------------------------------------
 AFS           2004-02-10-10.30      2004-08-18-04.40    power shut down
 AFS           2004-08-20-11:12      2005-01-10-02.20    sensor calibration
 AFS           2005-01-11-01.43      2999-12-31-12.00    running
 AFU           2004-02-10-10.30      2004-08-15-02.22    power shut down
 AFU           2004-08-20-11:12      2005-01-10-02.20    sensor calibration
 AFU           2005-01-11-01.43      2999-12-31-12.00    running
 SCA           2004-10-21-10:20      2999-12-31-12.00    running
 SCB           2004-10-21-10:20      2999-12-31-12.00    running


sekar.m_core
 DATA_ID     AUTHOR             DATA_NAME
--------------------------------------------------------
 35332292    Frank Vernon       Anza  Sensor Data
 35332293    Kent Linquist      South Cal  Sensor Data

GUID 

A Globally Unique Identifier or GUID is a pseudo-random number used in many software applications. While each generated GUID is not guaranteed to be unique, the total number of unique keys (2128 or 3.4028×1038) is so large that the possibility of the same number being generated twice is very small.

Logical Resource 

A logical SRB resource is a SRB Resource that is derived from Physical Resources. A logical SRB resource might be derived with further constraints on a registered physical resource or by combining more than one physical resource as an entity. For example, if a physical resource 'A' is defined using a particular directory in a HPSS, a logical resource A-bar might be defined as a resource that restricts to a further sub-directory in 'A'. A 'logical SRB resource set' is kind of logical SRB resource. It is defined as a set of physical SRB resources. The aim is for this is to give a unique (logical) name to a set of resources and when SRB opens or writes a buffer to the logical resource it opens or writes to every resource in that set. A logical resource containing multiple physical resources can be treated as a 'single' resource when using it.

MCAT 

The MCAT is the Metadata Catalog. It is a database (using a DBMS) and contains all the information the SRB needs to function. This includes the location and physical path to each individual Data object (file), user and group information, and system and user defined metadata. Also see the MCAT Section in the FAQ and the MCAT writeup.

Physical Resource 

see Resource

Resource 

In the terminology of SRB, a resource is a software/hardware system that provides the storage functionalities. For example, HPSS can be a resource, as can a Unix file system. The term is equivalent to "Physical Resource". Logical Resources and Compound Resources are composed of multiple physical resources.

System Metadata 

MCAT considers five kinds of entities as primitive objects on which it keeps additional information. These are: data objects, resources, collections, users and methods. The system-level MCAT meta data items are these primitive objects and others derived from these.

User Group 

A user group is a uniquely identifiable name given to a set of SRB registered users.

User-Defined Metadata 

User-defined metadata is information about SRB data objects that users can establish. In addition to the built-in System Metadata, users can set up and query user-defined metadata as attribute-value-unit triplets (accessible via the Sufmeta Scommand). The Extensible Schema is another way in which users can define and use metadata specific to their application. Also see the FAQ item, What is application level meta data?.