Có những vấn đề thực hiện khác nhau về sự hỗ trợ của một hệ thống kiểu mở rộng với các chức năng liên quan (hoạt động). Chúng tôi một thời gian ngắn tóm tắt hereP • Các ORDBMS động phải liên kết người dùng định nghĩa chức năng trong không gian địa chỉ của nó chỉ khi nó là cần thiết. | 724 Chapter 22 Object-Relational and Extended-Relational Systems Implementation and Related Issues for Extended Type Systems There are various implementation issues regarding the support of an extended type system with associated functions operations . We briefly summarize them The ORDBMS must dynamically link a user-defined function in its address space only when it is required. As we saw in the case of the two ORDBMSs numerous functions are required to operate on two- or three-dimensional spatial data images text and so on. With a static linking of all function libraries the DBMS address space may increase by an order of magnitude. Dynamic linking is available in the two ORDBMSs that we studied. Client-server issues deal with the placement and activation of functions. If the server needs to perform a function it is best to do so in the DBMS address space rather than remotely due to the large amount of overhead. If the function demands computation that is too intensive or if the server is attending to a very large number of clients the server may ship the function to a separate client machine. For security reasons it is better to run functions at the client using the user ID of the client. In the future functions are likely to be written in interpreted languages like JAVA. It should be possible to run queries inside functions. A function must operate the same way whether it is used from an application using the application program interface API or whether it is invoked by the DBMS as a part of executing SQL with the function embedded in an SQL statement. Systems should support a nesting of these callbacks. Because of the variety in the data types in an ORDBMS and associated operators efficient storage and access of the data is important. For spatial data or multidimensional data new storage structures such as R-trees quad trees or Grid files may be used. The ORDBMS must allow new types to be defined with new access structures. Dealing with large text
