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The flexible handling of attribute information is essential for a geo- 
graphic information system. SYSTEM 9 recognises four ways in which 
attributes can be used. Attributes can be related to a primitive (PRAT), 
to a feature (DRAT), to the geometry of a feature (CAT) (e.g. the area of 
a parcel or bearing and distance of a straight line), or to the attribute 
of a feature (IRAT). Attributes can be defined as mandatory (value must be 
assigned after feature assembly), required (value must be assigned before 
a partition is merged with a project) or optional (the attribute can be 
defined or can be empty). The values of calculated attributes are main- 
tained by the system (e.g. the area of a parcel will automatically be 
recomputed when the parcel boundaries are modified). 
IMPROVED DATA CAPTURE AND EDITING WITH THE SYSTEM 9 DATA MODEL 
In order to maintain the consistency and integrity of the SYSTEM 9 data- 
base, data capture and editing are treated as one process. The user still 
has the option to deal with one module separately if he needs to. Data 
capture is an application-independent process of collecting spatial data 
and related attribute information. The same procedures are used to collect 
data from existing maps (at the digitising station S9-D) or from aerial 
photographs (with the analytical plotter station S9-AP) or from the pack- 
age for the processing of field-survey information (on an edit station 
S9-E or digitising station S9-D). SYSTEM 9 provides, therefore, an inte- 
grated solution for data capture, editing and information processing, 
independent of the source of the input information. The only difference 
is the work phase of the station set-up. Fig 2 shows the general work 
flow for data capture and editing. 
  
Station set-up 
  
  
Primitive data Topologic checks Prompt for 
capture and and simple attributes of 
edit feature assembly simple features 
Prompt for 
Define complex features attributes of 
complex features 
  
  
  
Bulk load and edit of attributes 
  
  
Fig 2: General work flow for data capture and edit 
Spatial data capture is, in general, made up of the following phases: 
a) Initialisation: 
- Select a feature class 
- Select a feature assembly mode. The following modes are possible: 
e the user begins feature assembly by command; unassembled primitives 
can be stored in the database or in a local buffer 
e the system starts a new feature with each pen-up command; the 
primitives are stored in a local buffer 
e the system stores each primitive as a new feature 
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