Transparent file access (TFA) refers to the capability that provides an application with access to remote files as though they were local. The network file system NFS is an example of a protocol which provides a transparent file access capability. With such a mechanism, an application can usually be applied unchanged to files within a file system mounted from a remote file server. This is possible only if the application's access to files is by means of normal file system access procedures provided by the operating system for use by end user applications. A transparent file access capability is generally not available to applications which bypass normal file system access procedures and perform operations on files by directly accessing the mass storage device.
An application that uses a SQL implementation which accesses files exclusively by means of normal file system access procedures is able to access remote files by means of a transparent file access protocol. Figure 8.3 shows how this is accomplished. From the local workstation, a user mounts a remote file system located on a remote server. The database files needed by the SQL implementation on the TFA client are located within this remotely mounted file system. The X client application using the SQL implementation receives responses to its SQL statements as though the database files were local.
Some implementations of SQL do perform operations on files by directly accessing the mass storage device. Consequently, an application which uses such a SQL implementation is unable to make use of a transparent file access mechanism.