05-830, User Interface Software, Spring, 1997
Lecture 18,   April 30, 1997
Copyright © 1997 - Brad A. Myers

Component Technologies

Overview

• Andrew Toolkit, OLE, OpenDoc, Java Beans
• Goals:
  • Allow different applications to co-exist closely
    • Data from one to another be "active", unlike Cut and Paste
    • No need for an application to have a viewer for all kinds of data
    • Just invoke the right editor
  • Allow smaller applications because don't have to implement redundant functions
    • No need for Microsoft Word to implement a drawing program
    • PowerPoint and Excel can share a charting program
    • Reusable pieces
  • Allow applications from different vendors to cooperate
• Concepts:
  • Components -- Andrew "Insets" = OLE "Embedded Object" = OpenDoc "Parts" = Java "Beans"
  • Containers -- also called "Shells", "Frames", "Forms", what the components are embedded in.
  • Scripting -- initiate and direct interactions among components.  Might be regular programming in C/C++ or Java, or some kind of scripting language like Visual Basic, tcl, JavaScript, etc.
• Issues:
  • Sharing and Controlling the space: layout
  • Sharing and Controlling the menus, which might be global menubars
  • Sharing and Controlling the mouse pointer: who gets the clicks?
    • "Use" vs. "Mention" problem
  • How save contents to a file ("persistence")
  • How embed a new kind of object?
    • Pick from a list of all possible applications?
    • Components register themselves when loaded. (network?)
  • Need to dynamically load and link to the code of the new component
  • Drag and drop among components, and of components
  • OLE: How find out which protocols the component supports?
  • JavaBeans: How interface to an Interactive Builder?

Andrew Toolkit

• Previous guest lecture about Andrew
• Main development, 1985-1987
• Goal: embed any kind of editor inside of a text editor (recursively)
• Custom object system in C
• Embedding new kinds of objects: type in the Unix file name

OLE

• Microsoft's technology for components
• "Object Linking and Embedding"
• Quite complicated due to need to be
  • backwards compatible
  • language independent (multiple programming languages)
  • not shared address space
• Somewhat easier if use MFC framework rather than raw C  or C++ calls
• Based on "COM" = "Component Object Model
• also:
  • OLE Automation (control app from Visual Basic, etc.)
    • Also for spell checkers, EndNote, etc.
  • OLE Controls (how create new widgets, especially for use with Visual Basic
• Query OLE objects to ask them what "interfaces" (protocols) they support
• Then use the protocols for communication
• Embedded Object vs. Linked Object -- where the "real" data is
• "In-place activation" (not in OLE 1.0)
  • Double click to open
  • Modifies main menubars
• Renamed "ActiveX", which is a subset designed for use with the Web
  • Allows OLE controls to run inside Internet Explorer 3.0 and for regular applications
  • Java (or VB, Delphi, C, etc.) applications in an OLE wrapper
  • "Encapsulation" of components
  • Only runs on Win32 machines
  • Thousands of controls and components available
• http://www.microsoft.com/oledev/

OpenDoc

• From Apple
• Officially "CI Labs" consortium (with IBM, Novell, Adobe, 300 others...)
• Now officially not to be supported by Apple -- moving to Java instead
• All C++, so easier to use
  • True object system with inheritance
• Addresses some perceived shortcomings of OLE:
  • Overlapping and non-rectangular shaped frames
  • Editing of multiple objects at same time
  • Active ("Live") objects
  • Better network support (CORBA compliant)
  • Claims less development effort than OLE
• OpenDoc provides OLE compatibility
• Apparently renamed to be "Live Objects"
• http://www.opendoc.apple.com//
• http://cyberdog.apple.com  -- pretty cool network browser

Java Beans

• Component technology for Java
• Different from Applets, since Applets don't interact with each other
• Takes advantage of features of Java
  • Some added specifically to make components easier
  • "Platform Neutral" -- fully portable
  • Security for untrusted components
  • "Java Core Reflection" - for Introspection - to find out what methods a class supports
    • If follow "Design Patterns", then don't have to explicitly specify the interface
    • e.g., GetFoo, SetFoo for the foo property
  • "Java Object Serialization" - to store to files ("persistence")
  • AWT - for layout and graphics
• Goal: to be simple and small
• Can be easily integrated into a builder tool (and edit exposed properties)
• "Bridge" to OLE  and OpenDoc
• Uses CORBA and remote method invocation for networking
• "Real" support for networking and distributed computation
• Each component runs in a separate address space (for security)
• JavaBeans Development Kit (JDK), V1.1 as of Apr'97
• Implements a kind of constraints with property-change-listeners
• Future: Menubar merging
• http://splash.javasoft.com/beans/

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