Pitney Bowes MapXtreme - Manual (Page 592)

Appendix I: User-Defined Metadata
Metadata and the MapCatalog
MapXtreme v7.1 599 Developer Guide
Metadata and the MapCatalog
When working with spatial database queries, the MapCatalog has long been used as the sole
source of metadata when trying to infer accurate definitions for FeatureGeometry and Style columns
in the query result set. In some cases, however, the MapCatalog may not be a convenient,
appropriate, or reliable source. For example:
• Views–When defining view tables in the remote database server, the onus is upon the database
administrator to add a corresponding entry into the MapCatalog. This may be inconvenient, and
there is a risk of inaccuracy in the content.
• Stored Procedures–As a potentially dynamic generator of spatial result sets, it may not be
feasible to place a single, static entry into the MapCatalog that accurately represents all of the
result sets capable of being generated as output to invocations of the stored procedure.
L
Stored Procedure queries are currently supported for SQL Server only.
• Tables containing multiple spatial columns–Although spatial databases may allow for tables to
contain more than one spatial column, the MapCatalog schema currently only permits the
metadata to be defined for a single spatial column of a table.
• Complex queries–Even when the MapCatalog contains accurate information for base tables
referenced in complex queries, the inferencing logic may be unreliable for several reasons:
•
It may be difficult for the metadata inferencing logic to properly locate the correct metadata
(e.g., complex join queries).
• The MapCatalog metadata may be inaccurate due to functions applied on the geometries
(e.g., coordinate system transformations, buffering points, convex hull aggregations, etc.)
• The inferencing logic may not know how to properly reconcile metadata identified for two or
more base tables (e.g., UNION queries).
User-Defined Metadata Support for TableInfoServer Queries
The MapInfo.Data.TableInfoServer class contains properties that enable you to define metadata for
FeatureGeometry and Style columns in a table. This user-defined metadata, or column hints, identify
these columns in the absence of a MapCatalog.
ColumnHints Property
The ColumnHints property added to TableInfoServer gives users an explicit means of providing
user-defined metadata to influence the proper identification of FeatureGeometry and Style columns
in a query result set. These "hints" are principally intended for providing complete metadata in cases
where MapCatalog metadata could not be located; however, these hints may also be used as
potentially sparse definitions to selectively override components of the MapCatalog metadata. In
either case, user-defined metadata is considered definitive, so users are cautioned to use column
hints only when necessary, and when the details of the query results are well understood.