Hạn chế rất quan trọng trong quá trình làm mẫu nhằm Mỗi GI Cho đến giờ chỉ có nhận điều trị đặc biệt, tùy thuộc vào lĩnh vực ứng dụng và các công cụ được sử dụng. Trong bối cảnh năng động, với liên tục thay đổi thông tin địa lý, hạn chế được rất chủ đề; Bất kỳ trao đổi phát sinh nên tuân thủ các quy định ràng buộc, nếu không mâu thuẫn (dữ liệu lỗi chất lượng) sẽ xảy ra. Trong GIS, khó khăn là những điều kiện đó Luôn Must Be hợp lệ cho các mô. | Chapter 7 Constraints in Spatial Data Models in a Dynamic Context Peter van Oosterom GIS-technology Section Delft University of Technology Delft The Netherlands Introduction Constraints are important in every GI modelling process but until now have received only ad hoc treatment depending on the application domain and the tools used. In a dynamic context with constantly changing geo-information constraints are very relevant any changes arising should adhere to specified constraints otherwise inconsistencies data quality errors will occur. In GIS constraints are conditions that must always be valid for the model of interest. This chapter argues that constraints should be part of the object class definition just as with other aspects of that definition including attributes methods and relationships. Furthermore the implementation of constraints whether at the front-end database level or communication level should be driven automatically by these constraints specifications within the model. But this is not possible yet so this chapter will describe some implementation steps as interactively executed. In certain applications some functions linear programming in spatial decision support systems survey least squares adjustment cartographic generalisation editing topologically structured data etc. partially support constraints. However the constraints are not an integral part of the system and the constraint specification and implementation are often one and the same and deep in the application s source code. The result is that the constraints are hidden in some subsystems with other subsystems perhaps unaware of these constraints and it may be very difficult to maintain the constraints in the event that changes are required. This is true for G IS in general but is especially true for dynamic environments with changing objects where the support of constraints is required but presents a challenge. Example applications include cadastral or topographic data maintenance .
