Section 6: Mapping of Feature Attributes
6. Mapping of Feature Attributes
This section will describe the mapping of DLG-E feature attributes. Each of the feature types has a set of attributes that are required to describe a feature instance. The DLG-E Standards Database defines the set of feature types as well as its list of required attributes. The DPDF contains a set of attributes that apply to all feature types.
This section will describe the attribute mapping for some of the DLG-E feature types. For a complete listing of the attribute table design for each feature type refer to Appendix A.
6.1 Cases of Feature Attribution
The mapping of feature attributes will be described by studying a small set of feature types that include the cases encountered. Each case is described and then an example from DLG-E content is listed.
6.1.1 Common Feature Attributes
Each feature type, in addition to its specific set of attributes, has attributes that apply to all or many types. These common feature attributes can come from the Standards Database or from the DLG-E Portable Data File (DPDF).
From the DPDF:
From the Standards Database:
PHC Photorevision Category (used by 190 of 196 types)
(n/a on Route, Watercourse, Prime Meridian,
Connector, Junction, Underpass)
NAM Name (used by 114 of 196 types)
6.1.2 No Attributes
Feature Type: Shrubland
There are feature types that have a simple set of 1 or more attributes. None of its attribute values have attributes. None of its attributes can be multi-valued.
Feature Type: Aircraft Facility
Feature Type: Boundary Line
Feature Type: Mud Pot
6.1.4 Attributes on Attribute Values
There are feature types that have attributes on some of their attribute values. (Whether an attribute is to be valued is dependent on the value of another attribute. This is similar to the concept of functional or transitive dependence, where the value of one attribute depends on the value of another attribute.)
If more than one value is attributed, the attribute can be the same or different for each value. Currently all cases of attributed values are only 1 level deep.
Feature Type: Barren Land
Feature Type: Cultivated Cropland
**(Two values for the same attribute have different secondary attributes.)
Feature Type: Inundation Area
There are feature types with attributes that can have multiple values. For some feature instances, multiple values for the same attribute may be needed to describe it adequately.
Feature Type: Cable/Pipeline Site
There are feature types that mix multi-valued and attributed values.
Feature Type: Lake/Pond
**(A multi-valued attribute has two secondary attributes.)
Feature Type: Institutional Site
**(Both primary attributes are multi-valued. A primary attribute has the same secondary attribute for each value.)
All attributes from the Standards Database for feature types are encoded as SDTS user-defined attributes. None map to standard fields as was the case for the dataset, theme, and surface objects. (There are certain attributes that contain information of a data quality nature. These will be noted in the appropriate data quality module.)
The DPDF contains elements that apply to all feature types. Some are to be encoded and others not. The following table lists all of the common feature attributes from the DPDF in the left column and how they are mapped into the SDTS in the right column.
This section will describe how each of the cases of DLG-E feature attribution are encoded as SDTS attribute tables. The order will follow that of section 6.1.
The design of the attribute tables does not reflect a relational mapping. Functional dependencies among attributes based on values are not preserved by the table designs. Multiple tables for the same entity type are not joinable. The tables are set up so that an object points directly to all of its applicable attribute records. There is no relational joining needed to retrieve all of the attributes for an object. Investigations into a more relational mapping are under consideration.
As a general guideline, each feature type will have its own attribute table (as recommended by the Topological Vector Profile.) If the feature type has no attributes, then it will not have its own table. If the feature type has only name as an attribute, then it will not have its own table. If the feature type has multi-valued attributes and(or) attribute values with attributes, then it may have more than one attribute table.
6.3.1 Common Feature Attributes
There is one attribute table that will be shared by all feature types. It contains the elements from the DPDF to be encoded, as well as the Standards Database defined Photorevision Category (PHC) because it applies to all feature types.
The second attribute table will be used by feature types that only have name as an attribute, or have name as a multi-valued attribute.
Feature type Shrubland will not have its own attribute table. The instances of this feature type will be attributed in the Common Feature Attribute Table.
A single table is used for all of the attributes. If a feature type has only name as an attribute, then it uses the shared table. If a feature type has many attributes, then separate tables may be used to partition the attributes by subject.
Feature Type: Aircraft Facility
Feature Type: Boundary Line
Feature Type: Mud Pot
none
6.3.4 Attributes on Attribute Values
Feature Type: Barren Land
Both attributes are placed in the same table. When EAC value is not "Rock", then RKT value will be "not applicable." This is semantically equivalent to having attribute RKT apply only to the EAC value of "rock." A feature instance will reference one row from the table.
Feature Type: Cultivated Cropland
All attributes are placed in the same table. A not applicable value is used for both CPI and PLP or just one depending on the value of CCT. A feature instance will reference one row from the table.
Feature Type: Inundation Area
Two tables are used to partition two different attributes having secondary attributes. Elevation having secondary attributes of stage and source is a common pattern so it will be in its own table. The name attribute is grouped with the other attribute ICS and its secondary attribute IAT. A feature instance will reference one row from each table.
Feature Type: Cable/Pipeline Site
There is a single table for the attribute. A feature instance will reference multiple table rows when it has multiple attribute values.
Feature Type: Mine
The three single-valued attributes share a table and the multi-valued attribute PRD must be in its own table. (If PRD where with the other attributes then the only way to encode multiple values would be to repeat the row. This is not acceptable according to the Topological Vector Profile.) A feature instance will reference one row from the first table and one or more rows from the PRD table.
Feature Type: Survey Corner
Both attributes are multi-valued and not dependent on each other, so they each get a table. A feature instance will reference one or more rows in each table.
Feature Type: Lake/Pond
Elevation is multi-valued so it must go in its own table. Stage and source further describe elevation values, so for each elevation value there is a value for stage and source. The other attributes all share the same table. A feature instance will reference one row from the first table and one or more rows from the elevation table.
Feature Type: Institutional Site
The name attribute is multi-valued so the common table is used. A feature instance will reference one or more row from first table and one or more in the Name table.
|
U.S. Department of the Interior
|| U.S. Geological Survey 1400 Independence Road, Rolla, MO 65401 For general information call: (573)308-3500 URL: http://mcmcweb.er.usgs.gov/sdts/emapoct_93/section6.html Last modified: Monday, 14-Jan-2013 19:28:54 EST Maintainer: mcmcweb@usgs.gov Privacy Statement || Disclaimers || FOIA || Accessibility |