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605.707.3VL - Software Patterns

Computer Science

Spring 2024

Description

Software patterns encapsulate the knowledge of experienced software professionals in a manner that allows developers to apply that knowledge to similar problems. Patterns for software are analogous to the books of solutions that enable electrical engineers and civil engineers to avoid having to derive every new circuit or bridge design from first principles. This course will introduce the concept of software patterns, and explore the wide variety of patterns that may be applied to the production, analysis, design, implementation, and maintenance of software. The format of the course will emphasize the discussion of patterns and their application. Each student will be expected to lead a discussion and to actively participate in others. Students will also be expected to introduce new patterns or pattern languages through research or developed from their own experience. Programming exercises performed outside of class will be used enhance discussion and illustrate the application of patterns.

Instructor

Jon Lindberg

jlindbe2@jhu.edu

Course Structure

The course materials are divided into modules which can be accessed by clicking Home on the left menu. A module will have several sections including the overview, content, readings, discussions, and assignments. You are encouraged to preview all sections of the module before starting. Modules run for a period of seven (7) days. You should regularly check the Calendar and Announcements for assignment due dates. A final project is assigned at the beginning of the semester and is due at the beginning of the final module of the course.

Course Topics

Factory Method/Strategy/ Decorator

Composite/Iterator/ Refactoring

Template Method/ Abstract Factory/Builder

Singleton and Monostate/Proxy

Idioms and Pattern Languages

Adapter/Bridge

Mediator/Observer

Chain of Responsibility/ Memento

Analysis Patterns, Architectural Patterns and Antipatterns

Prototype/Command

State/Visitor

Flyweight/Interpreter/ Façade

Championing Patterns and Final Project

Course Goals

To recognize the use and applicability of software patterns and employ that knowledge to create solutions that increase the flexibility and maintainability of software. Understand the different types of patterns that apply to the stages of the software engineering process. Experience the tradeoffs between pattern-based and non-pattern-based solutions and the consequences of each pattern.

Course Learning Outcomes (CLOs)

Understand the form and content of design patterns, what is not included in the patterns and how they fit into object oriented software design.
Gain familiarity with the other types of patterns available including analysis patterns, architectural patterns and anti-patterns.
Determine when it is appropriate to use patterns.
Develop a deeper understanding of the fundamental concepts of object oriented programming and how patterns illustrate and reinforce them.
Develop the ability to think criticality about the structure of software.

Textbooks

Gamma, E., et. al. (1995). Design Patterns: Elements of Reusable Object-Oriented Software. New York, NY: Addison-Wesley

ISBN 0-201-63361-2.

Textbook information for this course is available online through the appropriate bookstore website: For online courses, search the MBS website at http://ep.jhu.edu/bookstore.

Other Materials & Online Resources

Other course readings are available through the eReserves link on Canvas.

Required Software

Students will need access to a Java, C++, or Swift compiler and whatever software development environment they are comfortable using. No particular version of Java or Swift is required, though students using C++ will need a version supporting C++-11. The CMake file specifies C++-20. Students should also have the ability to create and read zip files for packaging assignments to turn in. Students may use another language than Java, C++, or Swift to implement the assignments with permission of the instructor, though students will be required to adapt the assignment framework to that language on their own.

Student Coursework Requirements

It is expected that each module will take approximately 7–10 hours per week to complete. Here is an approximate breakdown: reading the assigned sections of the as well as some outside reading text (approximately 2-3 hours per week), listening to the audio annotated slide presentations (approximately 1 hour per week), and implementing programming assignments (approximately 3-4 hours per week), participating in course discussions (approximately 1-2 hours per week).

This course will consist of four basic student requirements:

Preparation and Participation (Module Discussions) (20% of Final Grade Calculation)

You are responsible for carefully reading all assigned material and being prepared for discussion. The majority of readings are from the course text. Additional reading will be assigned to supplement text readings. The initial discussion questions are provided for read-ahead in each module, but you are encouraged to pose your own questions related to the pattern and its use in the discussion threads. Remember also to participate in the discussion questions posted by the Discussion Leaders for the module.

A new question for each pattern will be posted each of five consecutive days during the module. Post your response to the question or to other students’ responses and ask follow-up questions. While everyone will not be able to respond to every question, it is expected that each student will participate in the discussion of most questions during each module. Discussion on early questions may continue throughout the module.

Part two of your grade for module discussion is your interaction (i.e., Critical Thinking). Just posting your response to a discussion question is not sufficient; we want you to interact with your classmates. Be detailed in your postings and in your responses to your classmates' postings. Feel free to agree or disagree with your classmates or the instructor. Include insight from the text, the related pattern readings, and your experience implementing the pattern either in class or elsewhere. Please ensure that your postings are civil and constructive.

I will monitor and participate in the module discussions, but discussion should be directed primarily to the class rather than directly to me. It is the responsibility of the student with Discussion Leadership requirement for a pattern to summarize the overall discussions and post the summary for the module in the course Wiki. I will fill this role for patterns which are not chosen and for the patterns in Modules 1 and 2.

Evaluation of preparation and participation is based on contribution to discussions.

Preparation and participation is evaluated by the following grading elements:

Timeliness (20%)
Breadth of Participation (30%)
Critical Thinking (50%)

Preparation and participation is graded with the formula (2T+3B+5C)/3 and the following point values:

Discussion Grading – Points accumulate to 10 for each assignment.
Points	0	1	2	3
Critical Thinking	Statements contribute no new ideas, have minimal depth & detail. Rehashes or summarizes others. Unclear if student grasps topic. Mostly agrees or asks questions.	Contributes few new ideas. Statements contain some rehashing or summary of others. Seems to grasp discussion topic at least superficially.	Statements offer some depth and insight and some new ideas. Shows an understanding of the discussion topic.	Statements are consistently in depth and detailed with new, insightful ideas clearly connected to the topic. Demonstrates a command of the discussion topic.
Breadth of Participation	Contributes to one discussion.	Contributes one or two discussions and the discussion leadership.	Contributes to a majority of discussions including discussion leadership.	Contributes to all daily discussions.
Timeliness	No posts until near due date.	First post in second half of module. No further participation.	First post within first three days of module, i.e., no later than Thursday. Little or no further participation.	First post within first three days of module. Continued regular participation for remainder.

Assignments (30% of Final Grade Calculation)

Assignments generally require the development of a software solution implementing each of the patterns being discussed in the module. A small number of assignments may be completed by clearly describing how the existing implementation in the provided software framework already fully realizes the pattern, identifying which objects, methods and relationships fulfill all of the roles in the pattern to receive all 10 points for the pattern. One or two of the assignments may be completed by providing a strong and convincing argument for why the requested implementation of the pattern is not appropriate with reference to the pattern’s consequences. As noted in the assignment instructions, asserting that the scope of the project is not large enough to merit the use of the pattern is not sufficient reason to not implement the pattern.

All assignments are due according to the dates in the Calendar.

Late submissions will be reduced by one letter grade for each week late (no exceptions without prior coordination with the instructor). Extensions to a definite date will be granted if requested prior to due date.

If, after submitting an assignment you are not satisfied with the grade received, you are encouraged to redo the assignment and resubmit it. If the resubmission results in a better grade, that grade will be substituted for the previous grade, but treated as if it were submitted one week late.

Each pattern in the assignment will be rated by the following points, and all patterns in the assignment averaged together. Points may also be deducted for renaming framework files or submitting object files.

Assignment Grading – Points accumulate to 10 for each assignment.
Points	0	1	2	2.5
Structure	Structure does not match the canonical form of the pattern or of any reasonable alternative.	Structure deviates significantly from the canonical form in a way that does not preserve the intent of the pattern.	Structure follows the canonical form to a large part, but is missing one or more important features without justification.	Structure faithfully follows the canonical form of the pattern or of an alternate form that strictly matches the intent of the canonical solution.
Clarity	Roles of objects, classes, methods and relationships participating in the pattern are not clearly identified.	Some roles are identified, but it is not clear how they relate to others.	Most roles are evident. New classes, variables and functions are named in a way that makes their role clear.	All roles in the pattern are clearly identified.
Appropriateness	The pattern is used in place where it does not fit, or where there is an existing implementati on already.		The pattern is used to solve an appropriate problem, but ignores a pre-existing implementation.	The pattern’s use is completely appropriate to the circumstances.
Functionality	The implementation could not be made to work as attempted, even with an indefinite time for debugging.	The implementation is correct in the broadest sense, but has significant flaws. For example, there is an abstract Strategy and concrete Strategies, but there is no Context, or the Context has inappropriate knowledge of the concrete Strategies.	The implementation is mostly correct, but omits one or more important details, especially with regard to issues raised in the discussion but not mentioned by the text.	The implementation fully implements the pattern and any attendant details, e.g., initialization of Factory Method.

Final Project (30% of Final Grade Calculation)

The final project is a paper on one of two topics, either presenting an analysis of the use of patterns or potential for pattern use in a piece of open source software, or the documentation of an original pattern. For the first option the software must meet the following requirements:

It must be open source. I should be able to find the source online myself.
It must not be written by any of the following people: yourself, friends, co-workers, fellow students, the instructor.
The software must be written in a language that the instructor can understand: C, C++, C#, Java, Ada, csh, Executable UML. I’ll consider others like LISP or Scheme but prefer not.
The software must be sufficiently complex to support a rich set of patterns. What usually works best is to find a medium size program and to focus on one part of it.

The project is evaluated by the following grading elements:

The architecture of the software (UML diagrams are encouraged). This is a description of the overall purpose of the software, the high-level structure, and where in that structure is the software containing the patterns that you will discuss. (10% of the content)
Patterns encountered in the software or that should be applied to the software. This should include patterns at all levels from architecture to idiom. It is preferable to concentrate on 3-5 patterns and treat them in depth than to gloss over many. (50%) Discussion should include:
1. Implementation topics discussed in class such as the boundary conditions of the pattern (e.g., how is a Strategy initialized or when is a Singleton destroyed)
2. Differences from the canonical implementation
3. If the structure is similar to another pattern, why it is one vs. the other
4. How coupling is reduced and cohesion increased by the pattern’s implementation
5. How modularity and flexibility are improved by the pattern
Appropriateness of the patterns, i.e., was the pattern used appropriately in the software, matching the intent given by the GoF. Or if you are discussing the application of patterns to the software, justify their use. (40%)

The pattern analysis form of the final project is graded using the formula (Arch+5Patterns+4App)/3 with points assigned as follows:

Project Grading – Points accumulate to 10 for each assignment.
Points	0	1	2	3
Architecture	Superficially describes the software focusing mostly on how the software is used instead of on its structure	Describes the software but focuses on details unimportant to understanding the use of the patterns identified	Describes the software purpose and overall structure but does not identify where the patterns fit	Completely and concisely describes the software purpose and structure in relation to the selected patterns
Patterns	No more than one pattern other than Singleton or Strategy is identified. Few aspects of the pattern implementation are addressed. Pattern roles are not identified.	Less than three different patterns are identified after discounting Singleton and Strategy. Some aspects of the pattern implementation discussed in class are addressed. Some of the patterns’ roles are correctly identified.	Fewer than five different patterns are identified, or five patterns include both Singleton and Strategy. The critical aspects of the pattern implementation are addressed. Most of the patterns’ roles are correctly identified.	Five different patterns are identified only one of which is Singleton or Strategy. Most aspects of the pattern implementation discussed in class are addressed. All of the patterns’ roles are correctly identified.
Appropriateness	No critical judgement of the software author’s use of patterns is demonstrated.	One or two patterns are a strong fit.	Most patterns identified are a strong fit for the problem they solve, but inappropriate pattern solutions are not addressed.	Each pattern identified is a strong fit for the problem it is solving with substantiating reasoning, or the description clearly identifies why it is not.

For the second option any type of pattern may be described of any type, design, analysis, architecture, anti-, etc. The following criteria must be met:

The pattern must be original. Due diligence must be performed to make sure that the name is not used by any existing pattern, even if the patterns are not the same.
The pattern description should include each of the following components: name, intent, motivation, applicability, solution with structure and participants/roles and collaborations, positive and negative consequences, implementation notes, sample code, known uses, and related patterns.
The known uses should be working systems or systems in development. They need not be publicly available, but should not be solutions created solely to justify the pattern. There should be at least two known uses, preferably three.
There is no preferred length for the pattern; reference the variety of lengths of the patterns in the text.

The pattern creation form of the final project is graded using the formula (A+B+C+3D+3E+2F+2G+2H+I)/4.8 with points assigned as follows:

Project Grading – Points accumulate to 10 for each assignment.
Points	0	1	2	3
A. Intent	Intent is missing	Requires more than two sentences to describe the pattern, or is ambiguous		Clearly and succinctly describes purpose of pattern
B. Motivation	Motivation is missing	Describes an inapplicable situation	Describes a contrived situation	Describes a common situation that the pattern fits
C. Applicability	Applicability only restates the intent or motivation	Describes the problem being solved but not the specific qualities, for example describing Strategy as being applicable when there are multiple algorithms	Partially describes the specific qualities of the problem solved by the pattern	Describes the specific nature of the problem to which the pattern applies, for example describing Strategy as being applicable when there are multiple algorithms distinguished by the type of object that can be changed without affecting the client
D. Solution	Omits one or more of the roles, structure, or collaborations	Includes all three aspects of the solution but omits multiple necessary details	Includes all three aspects but omits a few details	Clearly identifies all roles, relationships, and collaborations
E. Consequences	Has only positive or negative consequences	Both consequences are described only one or fewer are non-trivial	Both positive and negative consequences are described but not all of them are relevant or non-trivial	Gives multiple positive and negative consequences
F. Implementation	No implementation considerations are described	Few or trivial considerations are described		Describes each of the design tradeoffs that must be considered when implementing the pattern
G. Sample Code	No sample code provided	Sample code is incomplete or does not match motivation	Sample code “works” but does not employ all of the elements of the solution described by the pattern	Simple software implementation applied to the situation described in the motivation
H. Known Uses	No known uses are identified	Known use is retrofitted to justify the pattern	Only one known use is identified	Identifies three specific places where the solution described in the pattern occurs
I. Related Patterns	No related patterns are iidentified	One or more patterns are identified but with a tenuous relationship to the new pattern	Only one relevant related pattern identified	Identifies at least two patterns that aid in implementing the new pattern or which are themselves aided by the new pattern

Discussion Leadership (20% of Final Grade Calculation)

Each student must provide supplementary materials and questions to support leadership of the discussion of one pattern during the semester. If there are more students than patterns available to lead, some duplication will be permitted.

There are three parts to leading a discussion.

Real world example, using props or video. This example should be different from the one provided in the paper from AG Communications.
Software example of the pattern drawn from an actual program design or implementation.
Providing at least one additional question to motivate understanding of the pattern.

Discussion leadership is graded as follows:

Discussion Lead Grading – Points accumulate to 10 for each assignment.
Points	0	1	2	3.3
Real World Example	The real world example is a poor analogy for the pattern. It is not clear what roles the pattern components play in the example.	The real world example is a close analogy to the pattern, but differs in one or more important aspects that are not called out by the discussion.	The real world example is a very close analogy to the pattern, but one or more of the abstract parts of the pattern are missing.	The real world example is a very close analogy or counter example for the pattern, and all roles described for the pattern are captured.
Software Example	The software example does not include the pattern or uses some other pattern instead.	The software example is appropriate, but is significantly incomplete.	The software example is appropriate, but some roles of the pattern are missing and not addressed by the discussion.	The software example is a complete expression of the pattern.
Demonstration of Understanding	Student is unable to answer nontrivial questions about the pattern and poses no questions not found in the discussion notebook.	Student is able to answer trivial questions about the pattern, but not questions requiring deeper insight. No new questions are posed.	Student is able to answer most questions about the pattern, and asks the class at least one insightful question.	Student is able to answer nearly all questions and requires little or no assistance from the instructor. One or more insightful new questions is presented to the class.

Grading Policy

Grading

Assignments are due according to the dates posted in the Canvas course site. You may check these due dates in the Course Calendar or the Assignments in the corresponding modules. I will post grades one week after assignment due dates.

I generally do not directly grade spelling and grammar. However, egregious violations of the rules of the English language will be noted without comment. Use of grammar or spelling that makes understanding of the work difficult or impossible will affect the grade.

A grade of A indicates achievement of consistent excellence and distinction throughout the course—that is, conspicuous excellence in all aspects of assignments and discussion in every week.

A grade of B indicates work that meets all course requirements on a level appropriate for graduate academic work. These criteria apply to both undergraduates and graduate students taking the course.

100–98 = A+
97–94 = A
93–90 = A−
89–87 = B+
86–83 = B
82–80 = B−
79–77 = C+
76-73 = C
72-70 = C-
69-67 = D+
66-63 = D

Final grades will be determined by the following weighting:

Item	% of Grade
Weekly programming assignments	30%
Discussion Leadership	20%
Final Project	30%
Participation in class discussion	20%

Academic Policies

Deadlines for Adding, Dropping and Withdrawing from Courses

Students may add a course up to one week after the start of the term for that particular course. Students may drop courses according to the drop deadlines outlined in the EP academic calendar (https://ep.jhu.edu/student-services/academic-calendar/). Between the 6th week of the class and prior to the final withdrawal deadline, a student may withdraw from a course with a W on their academic record. A record of the course will remain on the academic record with a W appearing in the grade column to indicate that the student registered and withdrew from the course.

Academic Misconduct Policy

All students are required to read, know, and comply with the Johns Hopkins University Krieger School of Arts and Sciences (KSAS) / Whiting School of Engineering (WSE) Procedures for Handling Allegations of Misconduct by Full-Time and Part-Time Graduate Students.

This policy prohibits academic misconduct, including but not limited to the following: cheating or facilitating cheating; plagiarism; reuse of assignments; unauthorized collaboration; alteration of graded assignments; and unfair competition. Course materials (old assignments, texts, or examinations, etc.) should not be shared unless authorized by the course instructor. Any questions related to this policy should be directed to EP’s academic integrity officer at ep-academic-integrity@jhu.edu.

Students with Disabilities - Accommodations and Accessibility

Johns Hopkins University values diversity and inclusion. We are committed to providing welcoming, equitable, and accessible educational experiences for all students. Students with disabilities (including those with psychological conditions, medical conditions and temporary disabilities) can request accommodations for this course by providing an Accommodation Letter issued by Student Disability Services (SDS). Please request accommodations for this course as early as possible to provide time for effective communication and arrangements.

For further information or to start the process of requesting accommodations, please contact Student Disability Services at Engineering for Professionals, ep-disability-svcs@jhu.edu.

Student Conduct Code

The fundamental purpose of the JHU regulation of student conduct is to promote and to protect the health, safety, welfare, property, and rights of all members of the University community as well as to promote the orderly operation of the University and to safeguard its property and facilities. As members of the University community, students accept certain responsibilities which support the educational mission and create an environment in which all students are afforded the same opportunity to succeed academically.

For a full description of the code please visit the following website: https://studentaffairs.jhu.edu/policies-guidelines/student-code/

Classroom Climate

JHU is committed to creating a classroom environment that values the diversity of experiences and perspectives that all students bring. Everyone has the right to be treated with dignity and respect. Fostering an inclusive climate is important. Research and experience show that students who interact with peers who are different from themselves learn new things and experience tangible educational outcomes. At no time in this learning process should someone be singled out or treated unequally on the basis of any seen or unseen part of their identity.

If you have concerns in this course about harassment, discrimination, or any unequal treatment, or if you seek accommodations or resources, please reach out to the course instructor directly. Reporting will never impact your course grade. You may also share concerns with your program chair, the Assistant Dean for Diversity and Inclusion, or the Office of Institutional Equity. In handling reports, people will protect your privacy as much as possible, but faculty and staff are required to officially report information for some cases (e.g. sexual harassment).

Course Auditing

When a student enrolls in an EP course with “audit” status, the student must reach an understanding with the instructor as to what is required to earn the “audit.” If the student does not meet those expectations, the instructor must notify the EP Registration Team [EP-Registration@exchange.johnshopkins.edu] in order for the student to be retroactively dropped or withdrawn from the course (depending on when the "audit" was requested and in accordance with EP registration deadlines). All lecture content will remain accessible to auditing students, but access to all other course material is left to the discretion of the instructor.