4.3         Attributes & Domains

Attributes add descriptors to the geometry of a feature. Attributes can contain information such as the name, type, or condition of a feature. For example, the attributes of a runway include its designator (e.g., 15R/33L), material type (e.g., concrete), and length (e.g., 6,500 feet). Figure 4-9 below shows a typical list of attributes associated with a Feature type.

Figure 4-9. Sample Attribute Table for a Feature Type

4.3.1            Common Attributes

Several attributes are common to all feature classes in this standard. Some of these are used for naming and identification purposes. Others provide a reference to the project that installed or first recorded the location of the feature. Other attributes provide additional information about the data. Following is a list of these common attributes (with the exception of common metadata attributes that are described in the next section:

A.      guid - A globally unique identifier (GUID) applied to each feature in the database for reference by GIS and other information systems. When GIS data are submitted to MDOT MAA and uploaded into the GIS Data Repository, each record will also be assigned a GUID, which means that no other records have the same identifier. Application modules will use this GUID to track features as they are modified. If users who download data encounter such GUIDs, they are required to retain the GUIDs and submit them, unaltered, with subsequent revisions, to the features they downloaded.

1.       The format of the GUIDs to be used is described in Figure 4-10 below. A numeric ID is used that contains the FAA region, airport location ID, feature type, date, and a timestamp. Since FAA region, airport location, and feature type are text values, corresponding numeric values have been assigned in the domain tables found in PEGS V1, Appendix 1E.1 Feature Types.

Figure 4-10. Format for Globally Unique Primary Keys

B.      maaId - A unique identifier used by people to refer to this feature (note: this is not a system primary or foreign key value). Refer to MDOT MAA’s Naming, Identification and Addressing Standard for additional requirements that may apply to the assignment of identifiers. If a feature class contains Confined Space attribute, see PEGS V1, Chapter 3.3.3.3 Structure ID for details of the Confined Space Structure ID format.

C.      maaAlias - An alternative or former name by which the feature is referred.

D.      status - A temporal description of the operational status of the feature.

E.       alternative - Discriminator used to tie features of a plan or proposal together into a version.

F.       projectType - The type of project or work activity that installed or first recorded the location of this feature. At MDOT MAA, projects can be carried out under Contracts, Tasks, Subtasks, Building Permits, and Installation Permits.

G.      projectId - A unique identifier associated with the project or work activity that installed or first recorded the location of this feature. These project IDs should conform to the following conventions.

1.       Currently MDOT MAA contracts are assigned numbers formatted as ORG-TY-YY-NNN, where ORG is a three digit identifier for the originating organization. In most but not all cases, this is “MDOT MAA”. TY is a two character indicator of the contract type. Key examples include “AE” for design contracts and “CO” for construction contracts. YY is a two digit representation of the year (e.g. 96 for 1996 and 02 for 2002). NNN is a unique sequential number that starts at 001 for the first contract of that type issues for a given fiscal year and is incremented by 1.

2.       AE Contracts can have zero, one or more tasks, tasks can have zero, one or more Subtasks. CO contracts can have zero, one or more tasks but do not have subtasks.

3.       Tasks under design contracts (referred to as design tasks) are assigned four digit task numbers that are unique to the design contract (e.g. 2412). Subtasks under design contracts carry the four digit task number and then a two digit sequential number after a decimal point (e.g. 2412.12). These task numbers were assigned sequentially starting at 1 in the early 1990s. Blocks of numbers are assigned to certain contracts, but not all may end up being used, so there is a possibility that task numbers have been skipped.

4.       Tasks under construction contracts (referred to as construction tasks) are assigned a sequential number that starts with 1 for each contract and is therefore not unique. These are not widely used outside of construction at MDOT MAA.

H.      userFlag – This attribute can be used for any purpose desired by the end user Often, this attribute is used to store relevant identifiers, notes or metadata that is accommodated elsewhere. The FAA’s Airports GIS also accommodates this attribute, so values entered into this attribute will be retained upon upload of required feature classes to the FAA.

I.        Confined Space – A field for specific Utility feature classes that may store features fitting the definition of a Confined Space.  This field shall be assigned the domain Code Boolean as defined and provided in PEGS V1, Appendix 1E.1 Feature Types, which will limit potential values to Yes, No, or <null>.

4.2               Domain Values

The values assigned to an attribute are sometimes limited. The range of acceptable values is referred to as the domain for that attribute. Domains that limit attribute values to a range of numeric or date values are referred to as range domains. List domains limit values to a selection of choices. If users can add values to a list of acceptable values and still be compliant with the standard, the list is referred to as a code list. A list that users cannot add to is referred to as an enumeration. In this standard, all of the list domains are enumerations. To distinguish attributes that are limited to a domain, the name of each attribute ends with “_D”. For each such attribute, there is an associated table in PEGS V1, Appendix 1E.1 Feature Types listing the acceptable values and their definitions.

4.3               Foreign Key Identifiers

Attributes containing primary key values of related records in other feature type tables are called foreign key identifiers. Foreign key identifiers provide a link between different types of features with logical relationships. For example, the data for a taxiway leading to a runway might contain a foreign key to the runway table that is populated with the primary key value for that runway.