standard) have tackled the issue of transferring the data 
schema gs well as the data. If taken up and successfully 
implemented, this approach would represent a significant 
step forward. In the update context, it would potentially 
make detached update more viable, as transfer of the 
data model (provided the update process can accept and 
use it) should allow the update process to update the 
data in terms of the model, performing the necessary 
integrity checks before returning the updated data to the 
master database. 
4.2 Data-centric v. Process-centric 
Alongside the progress towards "data-centric" transfer 
standards cited above, there is growing move towards 
"process-centric" standards. The motivation is to provide 
mechanisms for access to data where it sits, in its "local" 
format. Powerful stimulus for this approach is coming 
from the Internet community and the wider IT industry. 
The debate in the formal standardisation bodies (ISO 
TC211, CEN TC287) is still in progress, and the outcome 
is presently unclear, although the tide is moving in the 
process-centric direction. 
The same trend is apparent in the Update process, for 
the reasons stated in this paper. The need is for the data 
model to be accessed via the Application Programme 
Interface (API) ofthe spatial database. Object-orientation 
can provide a very clean interface at this level, 
particularly in terms of maintaining spatial database 
integrity, which is the increasingly dominant concern. 
The parallels between the activity of receiving and 
managing update information and the activity of issuing 
data and updates are apparent in the trends in 
technology and standardisation. 
5. CONCLUSIONS 
These trends are rapidly leading to a point at which the 
ability of update processes such as soft copy 
photogrammetry to deliver coordinate information and 
thematic interpretations is increasingly standardised, and 
in effect determined by the nature (resolution etc) of the 
available imagery rather than the processing available in 
the update tools. The utility of the update tools will rather 
be determined by their abilities to interact with 
increasingly complex data models, either in a detached 
mode via transfer formats that carry data model as well 
as data or in direct mode via the Open APIs of spatial 
databases with powerful data modelling capabilities. 
Increasingly these are following the Object-Oriented 
paradigm. 
Within this framework, progress can also be anticipated 
on spatial generalisation, in the short term by 
orchestrating the posting of updates between databases 
supporting different scale ranges. As the powerful 
conceptual framework of Object-Orientation provides 
more usable spatial generalisation functionality, 
increasingly scale-independent databases will become 
possible (e.g. across a band of scales), but update of 
958 
these will involve interactions with the underlying data 
models. These models must include provisions for 
metadata, and some appropriate mechanisms for 
recovery of history. The issues are trade-offs of system 
cost against data utility. 
As spatial databases cover wider areas and have richer 
content, so the requirement increases to issue data only 
to those entitled to it, to issue changes in a timely 
manner and to validate both content and updates. There 
is a growing need to devise means of managing change 
only (or incremental) update. Just as the balance has 
shifted from primary data capture to the implementation 
of updates to data already held, so it will shift further to 
the issuing of updates to the users or customers for the 
data. There are underlying common factors to both the 
receipt and the issuing of change information. A key 
concept is that of unique object-ids. Object-Oriented data 
models and database versioning provide powerful 
techniques for Spatial Database Update - a Key to 
Effective Automation. 
References from Books: 
Taylor, David A. (1990). Object-Oriented Technology: A 
Manager's Guide. Addison-Wesley Publishing Company. 
References from Other Sources: 
Ibbs, Tony J. (1995). Progress in the standardisation of 
geographic data - a U.K., European and International 
Perspective. IUSM Working Group on  GIS/LIS, 
Hannover, September 25-28, 1995. 
Woodsford, Peter A. (1995). The Significance of Object- 
Orientation for GIS. IUSM Working Group on GIS/LIS, 
Hannover, September 25-28, 1995. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996