'$RCSfile: eml-constraint.xsd,v $' Copyright: 2000 Regents of the University of California and the National Center for Ecological Analysis and Synthesis For Details: http://knb.ecoinformatics.org/ '$Author: jones $' '$Date: 2001-07-31 16:24:37 $' '$Revision: 1.10 $' This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA eml-constraint This schema defines the integrity constraints between entities (e.g., data tables) as would be maintained in a relational database. These constraints include primary key constraints, foreign key constraints, unique key constraints, check constraints, and not null constraints, among potential others. Relational integrity constraint descriptors Describes the relational integrity constraints of a relational database. Describes the relational integrity constraints of a relational database. This includes primary keys, foreign keys, unique keys, etc. New in EML 2.0 Unique identifier The unique identifier of this metadata file or object. The identifier field provides a unique identifier for this metadata documentation. It will most likely be part of a sequence of numbers or letters that are meaningful in a larger context, such as a metadata catalog. That larger system can be identified in the "system" attribute. Multiple identifiers can be listed corresponding to different catalog systems. nceas.3.2]]> The 'identifier' field is derived from the eml-dataset meta_file_id filed in EML 1.4. Catalog system The catalog system in which this identifier is used. This element gives the name of the catalog system in which this identifier is used. It is useful to determine the scope of the identifier, and to determine the semantics of the various subparts of the identifier. Unresolved issue: can or should this be a URI/URL pointing to the catalog system, or just the name? nceas.3.2]]> New to EML 2.0. Integrity constraint Information about the integrity constraint being defined. Complete information needed to reconstruct this integrity constraint for enforcement in a system such as a relational database management system. New in EML 2.0 type of constraint the type of constraint being defined the type of constraint being defined. This is what kind of constraint this is. PrimaryKey, ForeignKey, UniqueKey New in EML 2.0 constraint name name of the field that this constraint is tied to name of the field that this constraint is tied to. This could also be the name of an independent constraint such as a trigger or an autonumber generator. LocationID, TABLE1_NUMBER_GEN1 New in EML 2.0 constraint description description of the constraint description of the constraint. Any additional information that may be needed to fully understand the constraint. New in EML 2.0 table to which this constraint is tied table to which this constraint is tied table to which this constraint is tied. In the instance of a key, it is the name of the table in which it is defined. site_properties New in EML 2.0 Key The set of attributes to which this constraint applies. The set of attributes to which this constrint applies. For a primary key or a unique key, the set of attributes must be identifying. For a foeign key, the set of attributes must match an identifying key in the referenced entity. For a not null constraint, the key indicates the attribute which should not be null. New in EML 2.0 Referenced Entity ID The id of the parent-entity in a foreign key constraint. This field contains the id of the entity to which a foreign key refers, otherwise known as the parent-entity or parent-table. site_properties New in EML 2.0 Key The set of attributes to which a foreign key constraint refers. The set of attributes to which a foreign key constraint refers. If the key refers to the primary key in the referenced entity, then the "referencedKey" is optional. For a foreign key, the set of attributes must match an identifying key in the referenced entity. New in EML 2.0 Constrint Cardinality The cardinality of a foreign key constraint. Indicates the cardinality (zero, one, many) of a foreign key constraint. New in EML 2.0 Check Condition A SQL statement to be used as the condition for a check constraint. A SQL statement to be used as the condition for a check constraint. Generally this provides a means for constraining the values within and among entities. 1900 and year < 1990)]]> New in EML 2.0