How to Implement HDFView Modules

Table of Contents

• 1. Introduction
  • 1.1 What is modular HDFView?
  • 1.2 Why modular HDFView?
  • 1.3 Basic requirements
• 2. Fundamental approach
• 3. How to implement an I/O module
• 3.1 Classes to implement
• 3.2 Steps to implement an I/O module
• 4. How to implement a GUI module
• 4.1 Replaceable GUI components
• 4.3 Steps to implement a GUI module

1.Introduction

1.1 What is modular HDFView?

• File I/O (already implemented)
• Image view
• Table view (a spreadsheet-like layout)
• Text view
• Metadata (metadata and attributes) view
• Tree view
• Palette view

1.2 Why modular HDFView?

• Separation of file I/O and data viewer: GUI components do not depend on file I/O implementation. Adding a new file format does not need to change any of the GUI components.
• Replaceable GUI modules: users can implement their GUI components to replace the default implementation of the TreeView, TableView, ImageView, etc without change of any other code. The development of use modules and HDFView are independent.
• Reuse source code: users can extend their classes from common packages and abstract classes for less coding.
• Configurable installation: users can choose to install HDF4 support or HDF5 support or both.
• Easy to maintain: replacing/changing one module does not change the rest of the source code.

1.3 Basic requirements

• Separate file I/O access and GUI components so that adding a new data format does not require changing the GUI, and vice visa.
• Provide abstract interfaces/classes along with a default implementation.
• Dynamically load user's modules: automatically detect user's module, which is packed in jar files
• Provide a mechanism for users to select which module to use when multiple modules are provided.
• Extensive documentation and examples on how to implement such a module.

2. Fundamental approach

The HDFView consists of three basic components: the main view, the object package, and the GUI modules. The following figure explains the relationship of the three components.

The main window is the first window frame you see when you start the HDFView. It has access to only to the the common object package (abstract data object classes) and the GUI interfaces. It does not depend on any implemwntation of theI/O and GUI components. Therefore, adding new modules does not require any change in the HDFView. This will separate user's implementation from the HDFView development.

The layout of the main window is shown in the following figure. The main window has two major panels: the TreeView Panel and the Data Panel. The TreeView Panel is used to display the structure of the file in tree. The Data Panel is used to show onther GUI components such as ImageView, TableView and TextView.

The common object package, ncsa.hdf.object, consists of abstract classes for file access. The abstract classes only define abstract methods such as data input/output from/to file. Sub-classes have to implement these interfaces. The HDFView only depends on the abstract classes. For example, when you open a file from the HDFView, the main view calls the method, ncsa.hdf.object.FileFormat.open(filename) and retrieves the file structure. The details of how to open the file and how to retrieve the file structure are left for implementation classes.

GUI components, such as TreeView, ImageView, TableView, etc, are interfaces instead of implementing classes. The main view only access to these interfaces. For instance, when you launch a command from the HDFView to display a dataset in TableView, the HDFView calls TreeView.showDataContent(dataObject) and returns the implementation of the TableView of user's selection.

3. How to implement an I/O module

3.1 Classes to implement

To add new I/O module (file format), the following classes must be implemented.

• FileFormat
  FileFormat defines general I/O accessing interface to file resources, such as open/close file, and retrieve file structure. For details, read FileFormat.html. Two implementing classes, H5File and H4File, are provided for the HDFView to support HDF5 and HDF4 respectively.
• Group
  Group is an abstract class. This class includes general information of a group object such as members of the group, and common operation on the group. For details, read Group.html. Two sub-classes, H5Group and H4Group, are provided to represent HDF5 group and HDF4 group respectively.
• Dataset (ScarlarDS or CompoundDS or both)
  This abstract class includes general information of a dataset object such as datatype and dimensions, and common operation on the dataset such as read/write data values. Dataset has two abstract subclasses: ScalarDS and CompoundDS. User's classes must inherit from either ScalarDS or CompoundDS. For details, read Dataset.html.

3.2 Steps to implement an I/O module

• Download and install HDFView and and include $HDFVIEW/lib/*.jar files in your claspath
• Implement your I/O module (FileFormat, Group, and Dataset)
• Pack your binary classes in a jar file and put it at $HDFVIEW/lib/ext.
• If there is any required dynamic link libary, put it at your system path or at $HDFVIEW/lib/ext for the HDFView to detect it.
• Register the new dataformat in HDFView or property file. You only need to register the new dataformat once.
• Register the new FileFormat from HDFView: Start HDFView and go to "Tools" --> "Add File Format" and add the full class name of the FileFormat with a file extension and key associated to the file format.

  
  Register FileFormat from HDFView

• Register the new FileFormat from property file: start HDFView and close it if you never use the HDFView before. After the first use of the HDFView, it creates a property file, hdfview.props, at the user director. Add the new FileFormat in the property file in the form of
  module.fileformat.KEY=full_class_path.
  For example, the highlight line registers the H5File in the HDFView property file, C:\Documents and Settings\xcao\hdfview.props.

  
  Register FileFormat from Property File

4. How to implement a GUI module

4.1 Replaceable GUI components

• Tree view
  TreeView defines interfaces for displaying and operating file structure in the form of tree. When you open file, HDFView will invoke the selected tree view module and display the structure of the file on the tree view panel. User's module is responsible on the details of how the file structure is displayed and what action is take when a tree item is clicked. The default tree view displays the structure of the file in a tree with data groups and data objects represented as conventional folders and icons. Users can easily expand or collapse folders to navigate the hierarchical structure of the file.

  
  Default Tree View

• Table view
  TableView is a spreadsheet-like table to display numberic or string data values. The default table view provides very limited prreadsheet features.
• Image view
  ImageView is used to display images. The default image view is provided to display HDF4/5 images. it has very limited function of processing image. An HDF4 image is raster image of 8-bit pixels with and indexed RGB color table, or a 24-bit true color image. An HDF5 image is a dataset that confirms the HDF5 Image Specification (with atribute name="CLASS" value="Image"). The default image view supports two types of images: indexed and true color. Both indexed image and true color image have predefined attributes and data layout according to the HDF5 image specification.
• Text view
  TextView is like a note pad. It displays the content of a dataset, usually string-type datasets, in ASCII text. The default text view is a JInternalFrame with a JTextArea.
• Metadata view
  MetadataView shows metadata of objects. Metadata includes attributes, and other properties of the object. The default metadata view is a JDialog with a tabbed panel to show general information and attribue of a data object.

  
  Default Metadata View

• Palette view
  A palette or color table converts the logical colour numbers stored in each pixel of an image dataset, normally represented as RGB triplets, that can be displayed as image on the monitor. The palette view is for users to display and modify the values of the RGB pixels.


Default Palette View

4.2 Steps to implement a GUI module

• Download and install HDFView and and include $HDFVIEW/lib/*.jar files in your claspath
• Implement your GUI module (TreeView, TableView, ImageView, etc.)
• Pack your binary classes in a jar file and put it at $HDFVIEW/lib/ext.
• Restart the HDFView. The HDFView will automatically detects and load the new GUI module.
• Set default GUI modlue. By default, HDFView opens dataset with default GUI modules. You can change the default GUI modules by
  "Tools" --> "User Options" --> "Default Module"

  
  Set Default GUI Modules