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Annex C

(Informative)

Attribute Encoding

This annex presents a further explanation of the attribute encoding methods specified in the normative portion of the standard. Encoding examples, at the logical level, of the Attribute Primary and Attribute Secondary modules are given, together with examples of the Data Dictionary modules that describe the attribute data.

This annex also presents examples of valid attribute labels, and further describes the use of code sets. It presents a suggested list of code sets for use in a transfer.

C.1 Attribute Primary and Attribute Secondary Modules

The structure of an Attribute Primary module record is defined in 4.1.3.6.1, using BNF, as:

	<Attribute Primary module record>::= <module record identifier>
								[<spatial object ID>]
								[<attribute 1>]
								[<attribute 2>]
									.
									.
									.
								[<attribute n>]

		<module record identifier>::= <module name> <record id>

		<spatial object ID>::= <module name> <object id>

The spatial object ID field is optional. If used, it constitutes a backward link from the attributes to the spatial object. Forward links from the spatial object are made through the use of a foreign identifier in the spatial object module record named Attribute ID. This field is also optional, but the minimum requirement is that there be at least either a forward or a backward link.

The structure of the secondary attribute module record is nearly identical to the structure of the primary module record: the difference is the absence of the spatial object link field.

The following schematic example shows some spatial objects with primary and secondary attributes and their potential links. In the first example ("Bridges"), the Attribute Secondary module is used to handle values of the standard attribute 'Composition' with a one-to-many link between 'Composition' and the attribute 'Material' (i.e., each bridge is composed of more than one material). In the second example, primary attributes such as 'State', 'County', and 'Land Type' are given FIPS and DLG code equivalents.

Table 52 - Point-node module "Bridges"

Point-Node			Attribute ID		Spatial Address
MODN	RCID	OBRP	MODN	RCID	X	Y
Bridges	1	NP	BridgeAtts	81	etc.
Bridges	2	NP	BridgeAtts	82
Bridges	3	NP	BridgeAtts	83

Table 53 - Attribute primary module "BridgeAtts"

Attribute primary		Spatial object ID		Attributes
MODN	RCID	MODN	RCID	COMPOSITION	SPAN LENGTH
BridgeAtts	81	Bridges	1	A	300
BridgeAtts	82	Bridges	2	B	1200
BridgeAtts	83	Bridges	3	A	500

Table 54 - Attribute secondary module "BridgeComp"

Attribute Secondary		Attributes
MODN	RCID	COMPOSITION	MATERIAL
BridgeComp	27	A	Wood
BridgeComp	28	A	Concrete
BridgeComp	29	A	Steel
BridgeComp	30	B	Concrete
BridgeComp	31	B	Wood

In the above example, the link between the Point-Node and Attribute Primary module records is one-to-one, while the link between Attribute Primary and Attribute Secondary records is one-to-many.

The DLG example shows attributes for a set of polygons, with one Attribute Primary Module and three Attribute Secondary modules:

Table 55 - Polygon module "GlenEllen"

Polygon			Attribute ID		Ring ID
MODN	RCID	OBRP	MODN	RCID	MODN	RCID
GlenEllen	1	PR	GlenEllenAtts	11	etc.
GlenEllen	2	PR	GlenEllenAtts	12
GlenEllen	3	PR	GlenEllenAtts	13
GlenEllen	4	PR	GlenEllenAtts	14

Table 56 - Attribute primary module "GlenEllenAtts"

Attribute Primary		Spatial Object ID		Attributes
MODN	RCID	MODN	RCID	STATE	COUNTY	LANDTYPE
GlenEllenAtts	11	GlenEllen	1	California	Sonoma	Park
GlenEllenAtts	12	GlenEllen	2	California	Sonoma	null
GlenEllenAtts	13	GlenEllen	3	California	Sonoma	Land Grant

Table 57 - Attribute Secondary Module "States"

Attribute Secondary		Attributes
MODN	RCID	STATE	DLGCODE	STATEFIPSCODE
States	37	California	091.0006	06
States	38	Nevada	etc.

Table 58 - Attribute secondary module "Counties"

Attribute Secondary		Attributes
MODN	RCID	COUNTY	DLGCODE	COUNTYFIPSCODE
Counties	92	Sonoma	092.0097	097
Counties	93	Napa	etc.
Counties	94	Mendocino

Table 59 - Attribute secondary module "LandTypes"

Attribute Secondary		Attributes
MODN	RCID	LANDTYPE	DLGCODE
LandTypes	6	Land Grant	090.0113
LandTypes	7	Park	090.0130

C.2 Data Dictionary/Schema Module

Each Attribute Primary or Attribute Secondary module shall have an associated Data Dictionary/Schema module. The following is an example of the Data Dictionary/Schema module for the BridgeAtts and BridgeComp modules of the Bridge example (the sequence of the subfield mnemonics in the table corresponds to the sequence of the subfields in the module description table). The entity for this example is "Bridge," a standard SDTS entity.

Table 60 - Data dictionary/schema field

Module record number	Subfield mnemonic	Subfield contents
1	MODN	BridgesSchema
	RCID	1
	NAME	BridgeAtts
	TYPE	ATPR
	ETLB	BRIDGE
	EUTH	SDTS
	ATLB	SPAN_LENGTH
	AUTH	NCHA
	FMT	I
	UNIT	METERS
	MXLN	5
	KEY	NOKEY
2	MODN	BridgesSchema
	RCID	2
	NAME	BridgeAtts
	TYPE	ATPR
	ETLB	BRIDGE
	EUTH	SDTS
	ATLB	COMPOSITION
	AUTH	NCHA
	FMT	A
	UNIT	null
	MXLN	1
	KEY	FKEY1
3	MODN	BridgesSchema
	RCID	3
	NAME	BridgeComp
	TYPE	ATSC
	ETLB	BRIDGE
	EUTH	SDTS
	ATLB	COMPOSITION
	AUTH	NCHA
	FMT	A
	UNIT	null
	MXLN	1
	KEY	PKEY
4	MODN	BridgesSchema
	RCID	4
	NAME	BridgeComp
	TYPE	ATSC
	ETLB	BRIDGE
	EUTH	SDTS
	ATLB	MATERIAL
	AUTH	ASTM
	FMT	A
	UNIT	null
	MXLN	1
	KEY	PKEY
(Continued)

1 COMPOSITION in BridgeAtts is only part of a foreign key.

Note that in the above example there is one Data Dictionary/Schema module for two attribute modules, confirming that there need not be a one-to-one correspondence between Data Dictionary/Schema modules and attribute modules. Also note that there are two records for the attribute Composition, because it occurs in both the Attribute Primary and Attribute Secondary modules.

C.3 Data Dictionary/Definition Module

The Data Dictionary/Definition module defines the entities and attributes used in the Attribute Primary, Attribute Secondary and Data Dictionary/Schema modules.

The use of the Data Dictionary/Definition module is demonstrated with the following example:

Table 61 - Data dictionary/definition field

Module record number	Subfield mnemonic	Subfield vontents
1	MODN	DDDEF
	RCID	1
	EORA	ENT
	EALB	Lagoon
	SRCE	A dictionary of geography, Monkhouse
	DFIN	A sheet of salt water separated from ....
	AUTH	FDMA
	ADSC	Federal Mapping Authority
2	MODN	DDDEF
	RCID	2
	EORA	ENT
	EALB	Bridge
	SRCE	Canadian Council on Surveying and Mapping
	DFIN	A structure erected over a depression...
	AUTH	NCHA
	ADSC	National Charting Board, Report Q17-F...
3	MODN	DDDEF
	RCID	3
	EORA	ATT
	EALB	SPAN_LENGTH
	SRCE	Bridge Engineering Associates Inc.
	DFIN	Distance between bridge abutments...
	AUTH	SDTB
	ADSC	Spatial Data Transfer Board, publication...
(continued)

In this example the first two records contain entity definitions; the last record defines an attribute of the entity "Bridge." The four-character Attribute Authority codes such SDTB, FDMA, NCHA, would also be used in the Attribute and Entity authority subfields of the Data Dictionary/Schema module for the example transfer.

Table 62 - An example of wildcard character use in this module

Module record number	Subfield mnemonic	Subfieldcontents
1	MODN	DDDEF
	RCID	1
	EALB	*
	AUTH	FDMA
	ADSC	Federal Mapping Authority

meaning that the code FDMA as used in each Attribute Definition or Schema field refers to "Federal Mapping Authority" for all attributes ("*" meaning all).

C.4 Data Dictionary/Domain Module

The Data Dictionary/Domain module describes the valid domains for the attributes stored with the Attribute Primary and Attribute Secondary modules.

Table 63 - Data dictionary/domain module example

MODN	RCID	ATLB	AUTH	ATYP	ADVF	ADMU	RAVA	DVAL	DVDF
DDDOMAIN	1	COMPOSITION	SDTS	ALPHABET	A	null	VALUE	Steel	iron & carbon
DDDOMAIN	2	COMPOSITION	SDTS	ALPHABET	A	null	VALUE	Wood	xylem
DDDOMAIN	3	SPAN_LENGTH	FDMA	INTEGER	I	Meters	MIN	5
DDDOMAIN	4	SPAN_LENGTH	FDMA	INTEGER	I	Meters	MAX	300

The first two records contain the domain type of ALPHABET for the attribute "composition" of the entity "bridge"; the last two contain the upper and lower limits of the range for the attribute "Span_length" of the entity bridge. Note that "Steel" and "Wood" are not part of an enumerated domain, other alphabetic values are legal. With an ENUMERATED domain type, no other values would have been allowed.

C.5 Attribute Labels and SQL Keywords

The standard specifies that an attribute label shall not be identical to an SQL keyword.

Table 64 - The SQL keywords

ALL	FETCH	PASCAL
AND	FLOAT	PLI
ANY	FOR	PRECISION
AS	FORTRAN	PRIVILEGES
ASC	FOUND	PROCEDURE
AUTHORIZATION	FROM	PUBLIC
AVG	GO	REAL
BEGIN	GOTO	ROLLBACK
BETWEEN	GRANT	SCHEMA
BY	GROUP	SECTION
CHAR	HAVING	SELECT
CHARACTER	IN	SET
CHECK	INDICATOR	SMALLINT
CLOSE	INSERT	SOME
COBOL	INT	SQL
COMMIT	INTEGER	SQLCODE
CONTINUE	INTO	SQLERROR
COUNT	IS	SUM
CREATE	LANGUAGE	TABLE
CURRENT	LIKE	TO
CURSOR	MAX	UNION
DEC	MIN	UNIQUE
DECIMAL	MODULE	UPDATE
DECLARE	NOT	USER
DELETE	NULL	VALUES
DESC	NUMERIC	VIEW
DISTINCT	OF	WHENEVER
DOUBLE	ON	WHERE
END	OPEN	WITH
ESCAPE	OPTION	WORK
EXEC	OR
EXISTS	ORDER
(continued)

Examples of valid attribute labels are:

	TYPE, Z_09, VEGETATIONCODING, B, Q_A_1, ATTRIBUTE000000001. 

Example of labels that are not valid are:

	type, 1ATTRIBUTE, _SECONDATTRIBUTE, VALIDATTRIBUTELABEL, Q__ABC, VEGETATION 
CODE, soiltype, SQLERROR and COUNT.

C.6 Suggested Code Sets

The encoding of data content by the sender, based upon the following widely used code sets, will facilitate a more efficient transfer of meaning. It is not the intent of this standard to recommend the coding of all data content, but simply to employ existing code sets where applicable. These sets may be used with the "cs:" convention and the appropriate FIPSPUB number as a domain specification in the Data Dictionary/Domain module.

Each document in the list is preceded by a short subject for reference purposes only.

	CODE SETS
		Catalog of Widely Used Code Sets, FIPSPUB 19-1, 7 Jan 85.

	CONGRESSIONAL DISTRICTS
		Congressional Districts of the United States, FIPSPUB 9, 14 Nov 69.

	COUNTIES
		Counties, and County Equivalents of the States of the United States and District of Columbia, 
FIPSPUB 6-4, 31 Aug 1990.

	COUNTRIES
		Countries, Dependencies, Areas of Special Sovereignty and their Principal Administrative 
Divisions, FIPSPUB 10-3, 9 Feb 84.  Guideline for Implementation of ANSI Codes for the 
Implementation of Names of Countries, Dependencies and Areas of Special Sovereignty, 
FIPSPUB 104, 19 Sep 83.

	CURRENCY
		Codes for Representation of Currencies and Funds, ISO 4217, 15 Jun 78.

	DATES
		Calendar Date, FIPSPUB 4, 1 Nov 68.

	HYDROLOGIC UNITS
		Codes for the Identification of Hydrologic Units in the United States and Caribbean Outlying 
Areas, FIPSPUB 103, 15 Nov 83.

	LOCATIONS
		Representation of Geographic Position Location for Information Interchange, FIPSPUB 70-1, 14 
Nov 86.

	ORGANIZATIONS
		Codes for Identification of Federal and Federally Assisted Organization, FIPSPUB 95, 23 Dec 
82.

	PLACES
		Metropolitan Statistical Areas, FIPSPUB 8-5, 31 Oct 1984.  Guideline:  Codes for Names of 
Populated Places, Primary County Divisions, Other Locational Entities in the United States, 
FIPSPUB 55-1, 30 Dec 83.  Power Plant Identification:  Recommended Practice, IEEE 803-1983 
&IEEE 803A-1983.  Standard Point Location Code (SPLC) Continental Directory, National Motor 
Freight 102-E, 1 May 1984.  National Zip Code and Post Office Directory, U.S.#Postal Service 
Publication 65.

	STATES
		States and Outlying Areas of the United States, FIPSPUB 5-1, 15 Jun 70.

	TIME	
		Representations of Local Time of the Day for Information Interchange, FIPSPUB 58, 01 Feb 79.  
Representations of Universal Time, Local Time Differentials, and United States Time Zone 
References for Information Interchange, FIPSPUB 59, 1 Feb 79.