About validating metadata
Validating metadata is a task you typically perform only if you must create metadata that conforms to a metadata standard. Validate after completing an item's metadata but before handing off your work. For example, if you plan to publish an item's description to a metadata catalog, validate an item's metadata before you publish it.
In ArcGIS, metadata is created and validated following the guidelines of the metadata standard associated with the current ArcGIS metadata style. The ArcGIS metadata editor checks the information you provide as you edit the item's description. When you are finished editing the item's metadata, you can validate it against an XML schema. Click the Validate button in the Description tab to validate the item's metadata for your metadata style. The item's metadata will be tested using the XML Schema or the XML DTD specified by the metadata standard associated with the metadata style.
Administrators of metadata catalogs often require metadata to be valid according to a specific test before they will publish it. In this case, the catalog administrator's test is the requirement you must satisfy regardless of what the standard's rules are and what validation mechanisms are specified by the standard. After clicking the Validate button, you can change the XML schema that will be used to test the metadata by providing the location of the catalog's XML schema in the Validate Metadata tool's Schema URL parameter.
Validating an item's metadata is often an iterative process. You edit the item's metadata, then check if it is valid. After finding a validation error, you edit the metadata to correct the problem, save your changes, then validate it again. The information you provided to resolve the first set of issues may trigger other conditions causing additional information to be required. Once those issues are fixed, you may find another problem, and so on.
If your organization creates GIS resources and makes them available to others, you are often updating the data constantly. Current descriptions for these resources can be posted regularly—maybe even daily. After ensuring an item's metadata is valid, chances are the regular updates required to keep the metadata current with the properties of the item won't make the metadata invalid. However, if you want to confirm that the metadata for these items is valid before publishing their updated metadata, select all the items in ArcCatalog and use the Validate Metadata button on the Metadata toolbar to check them all at once.
How an item's metadata is validated
An ArcGIS item's metadata is always stored in an internal, Esri-defined format. Even if other standard-compliant XML elements are added to the item's metadata, they will still be combined with internal Esri-defined content stored in Esri-defined XML elements. As a result, the item's metadata cannot be directly validated using a metadata standard's XML schema.
To validate an item's metadata, it first must be exported from ArcGIS to the appropriate storage format, then the exported XML file can be validated. An ArcGIS metadata style can define how to export metadata from ArcGIS to a standard-compliant XML format and identify an XML schema that can be used to validate the exported file. A shortcut is provided in ArcGIS Desktop that prevents you from having to perform the export and validation steps separately. When you validate metadata using the Validate Metadata button on the Metadata toolbar or the Validate button in the Description tab, an item's metadata is exported and validated as determined by the current metadata style in one step.
When you use the Validate or Validate Metadata buttons, the Translator, Schema URL, and Namespace URI tool parameters are populated appropriately based on the properties of the current metadata style. Translator determines how the metadata is exported. Schema URL determines the XML schema used for validation. Namespace URI determines the XML namespace in the exported XML file that will be validated by an XML Schema, if appropriate. If you validate using an XML DTD, Namespace URI identifies the root element of the XML document that will be validated, which should match the root element specified in the DTD.
If you open the metadata validation geoprocessing tools from the Search window, or the ArcToolbox window, or you run the tools using Python, the metadata style is not consulted and default values won't be available for the tool parameters.
If the item you've selected in ArcGIS is a stand-alone metadata XML file that is already in the correct format for a metadata standard, validate it directly against the appropriate schema using the XML Schema Validation tool not using the Validate Metadata tool. XML files that follow a metadata standard's format contain no ArcGIS metadata that must first be exported before the content can be validated.