File System

This chapter describes the file system of Pen Point. The file system has been designed for compatibility with DOS and includes full support for reading and writing DOS formatted disks.

The following features are included in the file system:

• Hierarchical directories

• 32-character file names

• Memory mapped files

• OOPs APls

Both the process of remote file transfer, automatic installation and the interface to device drivers is based on the architecture of a hierarchical system of directories and files.

Pen Point's file system is based of the concept of a volume; three types of volume are supported:

• Memory resident

• Local disks

• Remote disks and servers

Memory resident volumes are naturally stored in RAM; RAM is always available to the application because it cannot be disconnected by the user.

Local and remote disks are available to Pen Point when an external diskette drive is attached to the pen-based hardware, or when attached to a network or communications link.

All volumes have root directories. The operating system and applications make extensive use of the subdirectory tree structure of the hierarchical file system to store and retrieve specific files.

7.1.1 File System Activities

The following file activities are shared with other operating systems:

• Creating, opening and deleting files on a volume

• Copying and/or renaming files and directories

• Moving files and or directories

• Moving the read pointer to a new location with a seek operation

• Modifying file and directory attributes.

Pen Point however also supports a number of unique file activities. Every file and directory can have application defined attributes. Pen-based hardware is

designed to be highly portable; therefore the operating system must manage random disconnection and reconnection to external volumes. Activities requiring access to external volumes are stored until connection is established.

Pen Point automatically performs file compression and decompression. The user may select the type of compression to be performed and even elect not to perform file compression.

7.1.2 Application Installation

The standard for application distribution is a 3.5-inch DOS formatted diskette.

Applications usually include an installation routine which automatically installs the application within the desired file structure for the user.

Drag and drop routines are also supported whereby the user may drag application objects over an installer.

7.1.3 Interaction with other File Systems

The file system contains information that is incompatible with the DOS File Allocation Table (FAT) system and this superset information must be managed by Pen Point to maintain cross file system compatibility. The following information is not supported by the DOS FAT system:

• Long file names

• Pen Point specific attributes

• Application defined attributes

If the files to be stored are to be retrieved and reused by Pen Point, the superset information must be retained; this data is therefore stored in an extra file in each directory for which superset information exists in the Pen Point system.

Pen Point will detect and recognize this information when the external volume is mounted.

Pen Point files are only stored on external volumes without the superset information, if those files are to be subsequently manipulated by DOS applications.

Note ---~---~

Compound documents (multiple documents composed in and managed by two or more applications), are managed via the file system. Pen Point stores embedded documents in subdirectories of the "containing" documents. The compound document is therefore stored and maintained as a single

directory, which permits copying and moving of documents without having to be aware of the contents of the document.

7.1.4 File Import and Export

Applications generally include a set of filters (routines to process and convert data from one format to another format), to facilitate file import or export.

Pen Point supports data compatibility in the following manner:

7.1.4.1 File Import

Files imported into Pen Point must be associated with an application. When a file is selected and copied/moved from a Disk Viewer window to the Notebook Table of Contents, Pen Point will query every application running on the system

whether the particular file format being imported can be supported. The user is presented with a selection list of the appropriate applications.

The application checks the file import type, which is passed as a parameter, against a list of known file types; a positive response places the application on the selection list presented to the user. If the application is selected, the import process is initiated and a new document is created.

7.1.4.2 File Export

When the user selects Export, Pen Point queries the document to determine the file formats it can write. A selection list is then presented to the user. The user selects a file format and destination, then initiates the export process.

Each application is aware of the file formats supported for export and presents a list of formats supported together with control information that will be used during the translation process. The application will also provide a suggested file name for the user, which may be overridden.

The selected exporting application receives, along with the instruction to export, information about the source file, destination file and translator to be used.