Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-5 PS95&96-MEF-L9-5 Dr. M.E. Fayad  Document Structure Goals Recursive Composition Glyphs Design Patterns: Composite Pattern

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-6 PS95&96-MEF-L9-6 Dr. M.E. Fayad  Document Structure: Goals & Constraints Maintaining the document’s physical structure Generating and presenting the document visually Mapping positions in the visual rendition to elements in the internal representation Using one set of formatting and manipulation mechanisms to deal with both text and graphics

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-7 PS95&96-MEF-L9-7 Dr. M.E. Fayad  Document Structure: Recursive Composition Q q Q q space composite (column) composite (row) composite (row) composite row Recursive Composition of text and graphics Object Structure for Recursive Composition Recursive composition is a common way to represent hierarchically structured information by building increasingly complex elements out of simpler ones.

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-8 PS95&96-MEF-L9-8 Dr. M.E. Fayad  Document Structure: Glyphs A Glyph is an abstract class. Its subclasses are specialized to support different graphical elements, both primitive (characters and images) and structural (rows and columns). Glyphs’ responsibilities: They know 1. How to draw themselves 2. The space they occupy 3. Their children and parent 4. A low-level presentation for themselves

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-9 PS95&96-MEF-L9-9 Dr. M.E. Fayad  Document Structure: Composite Pattern Recursive composition can be used to represent potentially complex, hierarchical structure Programming languages can’t express this concept directly Composite pattern is used to document the recursive composition technique as it manifests itself in object-oriented systems Composite captures the essence of recursive composition in object-oriented terms

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-10 PS95&96-MEF-L9-10 Dr. M.E. Fayad Goals & Constraints Encapsulating the Formatting Algorithm Compositor and Composition Design Patterns: Strategy Pattern  Formatting

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-11 PS95&96-MEF-L9-11 Dr. M.E. Fayad Representation and formatting are distinct: The ability to capture the document’s physical structure doesn’t tell us how to arrive at a particular structure. The editor must break text into lines, lines into columns, and so on, taking into account the user’s desires. Constraints : –Flexibility –Changeability –The user configurations Formatting = breaking a collection of glyphs into lines, breaking lines into columns, and breaking columns into pages. The terms formatting and linebreaking are used interchangeably.  Formatting: Goals & Constraints

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-12 PS95&96-MEF-L9-12 Dr. M.E. Fayad Formatting algorithms tend to be complex. The design of Lexi: –Easy to change the formatting algorithms at least at the compile- time, if not at the run-time as well. –Encapsulate the formatting algorithm in an object. This will isolate the algorithm and make it easily replaceable. More specifically: –Define a separate class hierarchy for objects that encapsulate formatting algorithms –The root of the hierarchy define an interface that supports a wide- range of formatting algorithms, and each subclass will implement an interface to carry out a particular algorithm –Then, we can introduce a Glyph subclass that will structure its children automatically using a given algorithm object  Formatting: Encapsulating the Formatting Algorithm

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-13 PS95&96-MEF-L9-13 Dr. M.E. Fayad  Formatting: Compositor & Composition Compositor Compose() SetComposition() Glyph::Insert(g, i) compositor.Compose() Composition Insert(Glyph, g, int i) Glyph Insert(Glyph, int i) children ArrayCompositor Compose() TextCompositor Compose() SimpleCompositor Compose() compositor composition Composition and Compositor Class Relationships

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-14 PS95&96-MEF-L9-14 Dr. M.E. Fayad Encapsulating an algorithm in an object is the intent of Strategy Pattern Compositors are strategies; they encapsulate different formatting algorithms A composition is the context for a compositor strategy  Formatting: Strategy Pattern Strategy Pattern The key to applying the pattern to a particular problem is coming up with general strategy and context interfaces that support a broad range of algorithms.

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-15 PS95&96-MEF-L9-15 Dr. M.E. Fayad  Embellishing the UI Goals & Constraints Transparent Enclosure Monoglyph Design Patterns: Decorator Pattern

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-16 PS95&96-MEF-L9-16 Dr. M.E. Fayad Two embellishments in Lexi’s user interface: The first adds a border around the text to demarcate the page of text The seconds adds scroll bars that let the user view different parts of the page Shouldn’t use inheritance to add embellishments to the user interface, why? –To achieve flexibility »to make it easy to add or remove these embellishments (especially at run-time) and without changing other classes  Embellishing the UI: Goals & Constraints

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-17 PS95&96-MEF-L9-17 Dr. M.E. Fayad Transparent enclosure combines the notion of: 1. Single-child (or single-component) composition and 2. Compatible interface Clients generally can’t tell whether they are dealing with the component and its enclosure, especially if the enclosure delegates all its operations to the component. But the enclosure can also augment the component’s behavior by doing work of its own before and after delegating an operation. The enclosure can also effectively add state to the component.  Embellishing the UI: Transparent Enclosure

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-18 PS95&96-MEF-L9-18 Dr. M.E. Fayad  Embellishing the UI: Monoglyph MonoGlyph Glyph Draw(Window) component Draw(Window) Scroller Draw(Window) Border Draw(Window) DrawBorder(Window) MonoGlyph Class Relationships

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-19 PS95&96-MEF-L9-19 Dr. M.E. Fayad Decorator Pattern The Decorator pattern captures class and object relationships that support embellishment by transparent enclosure. In the Decorator pattern, the term embellishment refers to anything that adds state or behavior to an object.  Embellishing the UI: Decorator Pattern

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-20 PS95&96-MEF-L9-20 Dr. M.E. Fayad  Supporting Multiple Look-and- Feel Standards Goals & Constraints Abstracting Object Creation Factories and Product Classes Design Patterns: Abstract Factory Pattern

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-21 PS95&96-MEF-L9-21 Dr. M.E. Fayad - The Lexi’s design goals are: To make it conform to multiple existing look- and-feel standards To make it easy to add support for new standards as they emerge - This is a portability issue  Supporting Multiple Look-and-Feel Standards: Goals & Constraints The Lexi’s Design must support ultimate flexibility: Changing Lexi’s look and feel at run-time

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-22 PS95&96-MEF-L9-22 Dr. M.E. Fayad Assumptions: A set of abstract Glyph subclasses for each category of widget glyph A set of concrete subclasses for each abstract subclass that implement different look-and-feel standards Lexi must distinguish between widget glyphs for different look-and-feel styles This can be achieved by abstracting the process of object creation  Supporting Multiple Look-and-Feel: Abstracting Objects Creation

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-23 PS95&96-MEF-L9-23 Dr. M.E. Fayad  Supporting Multiple Look-and-Feel: Factories & Product Classes return new MotiScrolBar GUIFactory CreateScrollBar() CreateButton() MotiFactory CreateScrollBar() CreateButton() PMFactory CreateScrollBar() CreateButton() MacFactory CreateScrollBar() CreateButton() return new MotiButton return new PMScrolBar return new PMButton return new MacScrolBar return new MacButton GUIFactory Class Hierarchy

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-24 PS95&96-MEF-L9-24 Dr. M.E. Fayad  Supporting Multiple Look-and-Feel: Factories & Product Classes (cont’d) Glyph Abstract Product Classes & Concrete Subclasses ScrollBar ScrollTo(int) Button Press() Menu Pupup() MotiScrollBar ScrollTo(int) MacScrollBar ScrollTo(int) PMScrollBar ScrollTo(int) MotiButton Press() MacButton Press() PMButton Press()

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-25 PS95&96-MEF-L9-25 Dr. M.E. Fayad  Supporting Multiple Look-and-Feel: Abstract Factory Pattern Abstract Factory Pattern Factories and products are the key players in the Abstract Factory pattern. This pattern captures how to create families of related product objects without instantiating classes directly The Abstract Factory pattern’s emphasis on families of products distinguishes it from other creational patterns, which involve only one kind of product object

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-26 PS95&96-MEF-L9-26 Dr. M.E. Fayad  Supporting Multiple Window Systems Goals & Constraints Encapsulating Implementation Dependencies Window and WindowRep Design Patterns: Bridge Pattern

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-27 PS95&96-MEF-L9-27 Dr. M.E. Fayad This is another portability issue. Lexi must support multiple windows Lexi is designed to run on as many platforms as possibe for exactly the same reasons we support look-and- feel standards  Supporting Multiple Window Systems: Goals & Constraints

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-28 PS95&96-MEF-L9-28 Dr. M.E. Fayad  Supporting Multiple Window Systems: Encapsulating Dependencies glyph->Draw(this) Glyph Draw(Window) Window Redraw() Iconify() Lower() DrawLine() ApplicationWindowIconWindow Iconify() DialogWindow Lower() glyph owner->Lower()

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-29 PS95&96-MEF-L9-29 Dr. M.E. Fayad  Supporting Multiple Window Systems: Window & WindowRep WindowImp DeviceRaise() DeviceRect(...) Window Raise() DrawRect(...) ApplicationWindowIconWindow DialogWindow imp MacWindowImp DeviceRaise() DeviceRect(...) PMWindowImp DeviceRaise() DeviceRect(...) XWindowImp DeviceRaise() DeviceRect(...)

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-30 PS95&96-MEF-L9-30 Dr. M.E. Fayad  Supporting Multiple Window Systems: Bridge Pattern Bridge Pattern The relationship between Window and WindowRep is an example of the Bridge Pattern. The Bridge Pattern allows separate class hierarchies to work together even as they evolve independently. The Bridge Pattern allows for maintaining and enhancing the logical windowing abstractions without touching window system-dependent code, and vice versa.

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-31 PS95&96-MEF-L9-31 Dr. M.E. Fayad ‘ User Operations Goals & Constraints Encapsulating the Request for a Service Commands and Histories Design Patterns: Command Pattern

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-32 PS95&96-MEF-L9-32 Dr. M.E. Fayad Lexi provides different interfaces for the following operations: –Creating a new document –Opening, saving, and printing an existing document –Cutting selected text out of the document and pasting it back in –Changing the font and style of selected text –Changing the formatting of text –Quitting the application –and plus many more... Lexi’s is also designed to support undo and redo of most but not all its functionality The challenge is to come up with a simple and extensible mechanism that satisfies all of these needs ‘ User Operations: Goals and Constraints

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-33 PS95&96-MEF-L9-33 Dr. M.E. Fayad ‘ User Operations: Encapsulating the Request of a Service Command Execute() PasteCommand Execute() if (document is modified) { save->Execute() } quit the application QuitCommand Execute() SaveCommand Execute() buffer FontCommand Execute() newFont paste buffer into document make selected text appear in newFont pop up a dialog box that lets the user name the document, and then save the document under that name save Partial Command Class Hierarchy

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-34 PS95&96-MEF-L9-34 Dr. M.E. Fayad ‘ User Operations: Commands & Histories Glyph Command Execute() MenuItem Clicked() command command->Execute() MenuItem-Command Relationship

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-35 PS95&96-MEF-L9-35 Dr. M.E. Fayad A command may delegate all, part, or none of the request’s implementation to other objects This is perfect for Lexi that must provide centralized access to functionality scattered throughout the application. ‘ User Operations: Command Pattern Command Pattern The Command pattern objectifies the request for service. It decouples the creator of the request for a service from the executor of that service.

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-36 PS95&96-MEF-L9-36 Dr. M.E. Fayad ’ Spell Checking and Hyphenation Goals & Constraints Encapsulating Traversal Traversal versus Traversal Actions Design Patterns: Iterator & Visitor Pattern

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-37 PS95&96-MEF-L9-37 Dr. M.E. Fayad The design problem involves textual analysis: –Checking for misspelling –Introducing hyphenation points where needed for good formatting. Constraints are similar to the formatting constraints Two pieces of the puzzle: –Accessing the information to be analyzed –Doing the analysis ’ Spell Checking and Hyphenation: Goals and Constraints

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-38 PS95&96-MEF-L9-38 Dr. M.E. Fayad ’ Spell Checking and Hyphenation: Traversal vs. Traversal Actions Command Execute() NullIterator First() Next() IsDone() CurrentItem() iterator return true Iterator Class & Subclasses return new NullIterator ListIterator First() Next() IsDone() CurrentItem() ArrayIterator First() Next() IsDone() CurrentItem() PreorderIterator First() Next() IsDone() CurrentItem() currentItem Glyph... CreatorIterator() root

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-39 PS95&96-MEF-L9-39 Dr. M.E. Fayad Iterator Pattern Iterator Pattern objectifies traversal algorithms over object structures. Visitor Pattern Visitor Pattern centralizes operations on object structures in one class so that these operations can be changed independently of the classes defining the structure. ’ Spell Checking and Hyphenation: Iterator & Visitor Patterns

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-40 PS95&96-MEF-L9-40 Dr. M.E. Fayad Summary Eight different patterns applied in the Lexi’s design: –Composite to represent the document’s physical structure –Strategy to allow different formatting algorithms –Decorator for embellishing the user interface –Abstract factory for supporting multiple look-and-feel standards –Bridge to allow multiple windowing platforms –Command for undoable user operations –Iterator for accessing and traversaling object structures –Visitor for allowing an open-ended number of analytical capabilities without complicating the document structure’s implementation

Copyright © Active Frameworks Inc. - All Rights Reserved - V2.0Document Editor - Page L2-41 PS95&96-MEF-L9-41 Dr. M.E. Fayad Discussion Questions 1. Define: Glyphs and Monoglyph 2. List the goals and constraints of: Formatting Support multiple look-and-feel standards User operations Embellishing the user interface 3. Explain how to achieve the goals for formatting