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Appendix C: DPDF Attribute List

This appendix contains a list of attributes that are to be included in the SDTS Data Dictionary for DLG-E. These attributes are elements from the DPDF that are to be encoded. The list is derived from the attribute table designs in this document. The attributes are also given definitions as these are required by the SDTS.

Appendix D: DLG-E Example Module Set

Appendix D: DLG-E Relationship Module Example

This appendix contains a section of a set of modules to illustrate feature attribution and encoding of relationships. The attributes for feature types stream, junction, lake/pond, and shoreline are used to illustrate feature attribution. The DLG-E is-composed-of relationship is used to illustrate mapping to a standard field. The DLG-E relationships of is-bounded-by and flows-to are used to illustrate the relationship encoding technique described in section 7.3.1.

Feature Object Encoding

There is a composite module, named FF05, whose records represent the basic feature objects. (From the DLG-E description, the basic feature objects are directly composed of spatial objects.) The field ATID references the attribute records that describe the feature object. The field FRID references the set of spatial objects that represent the spatial component(s) of the feature object.

Feature Is Composed Of Feature Encoding

As discussed in section 7.2.2 the DLG-E is-composed-of relationship maps to the standard field FRID of a composite record. Inspecting record 2 of module FF05, we see it is composed of the spatial object represented by record 23 of module PC02. Because the TVP has module naming conventions, we know the spatial object is a polygon. We could also find out the module type of any module name by inspecting the Catalog/Directory records (not included).

Feature Attribute Encoding

Next let's look at the attribute records which describe this feature object. Inspecting record 2 of module FF05, we see that it is described by record 19 of module AP09, record 42 of module AP21, and record 50 and 51 of module AP22. Let's look at each of these attribute modules to see what they are describing.

The Schema module DDSH contains records which describe each attribute table. The schema contains information about which entity a table describes, which attributes (i.e. column headings) are in the table, and the format, units of measure and maximum value length of each table column. There is a schema record for every column of an attribute table (i.e. every subfield of Field ATTP). The set of records 52 through 55 describe module AP09.

From record 52 of module DDSH, we see that the entity type for table AP09 is "FEATURE". The Primary Attribute module AP09 is the attribute table that is shared by all feature types (see sections 6.1.1 and 6.3.1). Record 52 is describing the attribute ENTITY_LABEL. The authority (field AUTH) for defining this attribute is the Topological Vector Profile. We would turn to that document to learn that the standardized attribute "ENTITY_LABEL" is used to encode entity type as a value, especially for entities that are not further attributed. The DLG-E attribute "feature type" maps to this standardized attribute.

Record 55 of module DDSH is describing attribute PHC. The authority for it is USGS/NMD and its definition is included in the transfer. The Definition module DDDF contains the definitions for all entity and attribute terms. Record 4 of DDDF defines entity FEATURE and record 85 defines attribute PHC.

What does each of the attribute modules referenced by record 2 of module FF05 describe? From using the Schema and Definition records, we find that module AP09 describes FEATURE, module AP21 and module AP22 describe LAKE/POND. Lake/pond has two tables because it has a multi-valued attribute as discussed in section 6.3.6.

One of the objectives of an SDTS transfer is to encode the data as well as its meaning. The transfer contains enough information to determine:

• The feature object represented by composite module record 2 is a lake/pond. It is two-dimensional, composed of a single polygon. It has been photorevised. It is named "Grand", contains water for most of the year, and is not artificially impounded. It has an average water elevation of 760 feet and a high water elevation of approximately 770 feet.

The module set also includes records for shoreline, junction, and stream/river feature objects. The feature attribution for each of these can be determined in the same manner.

Feature Relationships Encoded as Attributes

The DLG-E relationships of is-bounded-by and flows-to are used to illustrate the relationship encoding technique described in section 7.3.1. Table BR01 is for the entity "Feature Is Bounded By Feature". The format of caret ("^") means the column values are packed foreign ids. The attribute values are composite module records which happen to represent feature objects. The relationship instance in record 1 of module BR01 is between a lake/pond (FF05#02) and a shoreline (FF05#01). (For determining the feature type of a feature object represented with a composite record see the Feature Attribute Encoding description above.)

Table BR02 is for the entity "Feature Flows To Feature". Record 1 describes a stream/river (FF05#03) flowing to a junction (FF05#06), and record 2 describes the same junction flowing to a lake/pond (FF05#02). (An explanation of the flow modeling concepts in DLG-E which involves junctions is beyond the scope of this example. It is used here however to show a very typical set of flows to relationships.) Continuing to inspect the set of relationships, we find that the same lake/pond flows to a junction (record 3), and this junction flows to another stream/river (record 4).

Module Set Illustrating DLG-E Feature Attribution and Relationships

The attribute tables that encode relationships:

(END of Appendix D)

The End

of the

SDTS Mapping of

the DLG-E Model

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