Architecture Specification

An architecture specification is a document that roughly outlines the architecture for the software program. It is partly an API, in that it identifies some of the major classes/modules and their functionality. However, it is clearly impossible to write a complete API at the start of a project; as you continue to work on the program you will obviously add new classes/modules and change existing ones. Hence this is also a “design” vision document in which out outline your major architecture goals, such as multithreaded AI or the presence of a scripting language.

This is also a document that we are continually tweaking within this class. As most of you have worked on such a document before (in the introductory course), you know that it is hard to get the level of detail just right. You give too much detail, and then your decisions change. Or you give too little detail and your programmers cannot agree on what to do.

This is why our philosophy is to stick with some simple tools and not to go full-on with complex tools like UML. UML is very expressive, but if you go into too much detail, then your spending more time programming in UML (for an architecture that might change) than working on creating your game. Instead, your goal should focus more on understanding how your team members work together and less on all of the fine details of your class structure.

Table of Contents

Document Format

The architecture specification is a written document that describes a vision of the details of your final product, much like the gameplay specification. Indeed, these documents are very similar because they have the same audience; they are both internal documents written to allow team members to break-up and work in isolation. The primary difference is focus. The gameplay specification focused on game elements like mechanics and challenges. The architecture specification focuses on software elements like classes and program flow.

Like the gameplay specification, this file should be constructed with clear sections and subsections. You should make good use of font styles, font size, and other forms of formatting to make it readable. We suggest that you organize your document as follows.

Dependency Diagram

Recall our discussion of CRC cards in the introductory class. If you do not remember it, reacquaint yourself with the appropriate lecture. CRC cards represent your modules (or classes, depending on how you look at things). More importantly, these cards represent the interfaces that everyone on the team must agree upon. Anything not represented by a CRC card is unimportant, and can be “owned” by a single team member. This means that you want to keep the number of CRC cards to a minimum.

You will eventually give us details on the CRC cards describing your architecture. However, we want a visual summary at the very start of this document. The dependency graph or diagram shows each of the CRC cards and their relationship to one another. Draw a box for each module/card and put the name of the module in the box. Then draw an edge between any two modules that collaborate. If you are unsure of how to do this, see the examples below for more information. The edges can be either directed or undirected. If you choose directed edges, have the edge incoming to the class with the responsibility.

The dependency diagram should include both your own classes and the third-party libraries. We need to see how everything fits together.

Class-Responsibility Collaboration Divisions

Once you have the dependency diagram summarizing everything, we want you to present more detail about the various modules. As the architecture specification is a single written document, we are not asking for teams to turn in a set of index cards. Instead, present the CRC cards in table form, as shown in several of the examples below. In addition, for each table, teams should provide the following information.

  • A high-level, English description of what this module does.
  • Justification for why this card represents a single, coherent module.
  • Classification of the class/module as either model, view, or controller.

How you format this additional information is up to you. However, when designing your cards, you should think about the important design patterns we talked about in class.

Model-View-Controller Pattern

This design pattern separates data from the user interface, and both of these from the input controls. The CRC Cards should respect this design pattern. In other words, each one of the cards should fall into one, and only one, of these categories. This also means that you will need a minimum of three CRC Cards: one each for the model, view, and controller. While it is not required, we highly recommend that you annotate each card by the appropriate catagory.

[”>Entity-Component Pattern]

This is an optional pattern that is recommended if you find yourself wanting to use a lot of subclasses. It was touched on in the architecture revisited lesson. If you elect to use this architecture, then we leave it up to you on how to categorize the components/roles. You may even categorize them as a fourth category (beyond model, view, and controller), if you wish.

Third-Party Libraries (Optional)

We are not expecting you to write everything from scratch in this class. You are all using our game engine CUGL. In addition many of you are planning to keep Box2D as your physics engine. You may also want to add third party libraries for things that we did not add, like pathfinding, character AI, or fluid-based physics.

In this section, list all of the third party libraries that the teams plans to use, beyond those we provide. So you do not need to list CUGL or Box2d, but you are expected to list Liquid Fun or FireBase, or any other APIs not provided with CUGL.

When you list a third party library, we want one CRC card for the entire library. For the responsibilities, identify only what the library is responsible for in your game. Functionality not used by the game can be left out. The collaborators for these CRC cards are typically trivial (e.g. the library only collaborates with itself). However, some third party libraries provide you with an interface that you must subclass or implement in order to use the library. If any of the classes or modules designed in the previous section fit that decription, then you should list them as collaborators on the CRC card.

Activity Diagram

In the introductory course, we also discussed the notion of activity diagrams. Activity diagrams outline the flow of the application over time. This is key in time-critical pieces of software like games (16.7 milliseconds per animation frame).

Remember that activity diagrams work like flow charts, except that you can follow multiple paths at a time. Use synchronization bars to fork and resync your activities together. Teams should not need any more syntax than what we showed introductory course. If your team does not believe that you can express your activity diagram with this information, please contact one of the course staff for help, or post on Campus Wire.

In this section we only want one activity diagram. It does not have to be an activity diagram for the whole program. Just concentrate on the update loop. Features outside this loop, like the main game menu or initialization, can be ignored. The exception for this is if you have networking. You may wish to factor networking into a separate activity diagram.

The activity diagram should coincide with the CRC divisions. Every single responsibility from the previous section should appear in the activity diagram, unless it is outside the main update loop (e.g. menu selection). If an appropriate responsibility does not appear in the activity diagram, either remove it from the CRC divisions or add it to the diagram.

The reverse is also true; every major task in the activity diagram should correspond to some class responsibility. Some of these activities may be supported by a third-party library like Box2D. But if the responsibility corresponds to a class that you have created, it belongs in the section on CRC divisions.

With that said, we are not asking for a separate activity box for each responsibility. It is okay to collapse multiple responsibilities into a single activity to make this diagram easier to read.

Data Representation Model

As you know from the introductory course, data-driven design is an important part of game development. Much of your game content is stored externally in configuration files, level designs, and object scripts. While this data may not be part of the team’s software program, it is part of the game architecture. Therefore, it is important to confirm data formats early.

Create a separate subsection for each type of data file in the game. We are assuming that the game has at least two types of data files: 1)the saved game file and 2) the level file. You may have more (like an asset directory file), in which case the team should include those in this document as well.

For each file type in the game, clearly describe the file representation. This includes

  • The file format (e.g. JSON, XML, or other)
  • The information stored in the file
  • How this information is stored (e.g. the JSON or XML keys)

What files you are going to have can be determined within the team. However, we recommend that teams organize it as follows:

Saved Game File

If you are using a checkpoint save model, this could be as simple as player progress. If you are doing anything more complicated, you will need to list all of the state that you store. What must be stored and what can be recomputed (or reset)?

Level File

The level file is always the most complicated file in the game, typically much more so than the saved game file. It has to contain all of the world geometry, any trigger or script references (these may be separate files), and so on.

Some of you may choose to use the Tiled level editor. If you do, it is not enough to say that you are going to use the Tiled file format. You have to specify which format (Tiled supports both XML and JSON). You also need to explain all of the custom properties that you are adding to your objects.

This document is always in flux. We are not expecting you to get it 100% correct on the first draft. We ask that you make a reasonable attempt at the document.

Network Protocol

If your game is networked, you are converting your game state in to data and sending this data across the internet. This is another serialization format. What is your networking protocol and data format? See the Family Style example below for what we are asking for here.

Other Files

If the team havs any other files that we may have missed, please let us know. These may include

  • Asset directory (a list of all assets and default settings)
  • Triggers or behavior scripts
  • Character statistics (e.g. health, strength, etc.)
  • Physics geometry for an art file

We leave the format for how to specify these up to the team.

Application Restoration Plan

This last bit is necessary because you are all on mobile devices. As we discussed in the mobile memory lesson, mobile applications may or may not be suspended when the user returns to the home screen. The team should have a plan for how to suspend the application. Is all data lost and the user reloads? Or can you at least recover some of the previous state?

This problem is very similar to that of the previous section, but it is not serialization per se. Instead, teams have to think about the App restoration restoration API as defined in the Application Class Provide a description of how the team is going to use this API to handle App suspension and restoration.


This document is perhaps the hardest one to “get right” in this course. We have never found an architecture specification that we are 100% happy with. However, each of the specifications below are notable in some way. They are either very strong (but not perfect) or did one part of the specification very well.

You will note that all of the examples below put the dependency diagram after the CRC cards. We are asking you to reverse this order this year. We have long used the dependency diagram as a “table of contents” for the CRC cards, so it makes sense to do this first.

No Screws Attached

The most recent game on this list, the 2022 game No Screws Attached was a networked physics battler in the style of Tricky Towers. Since this game has networking, it needed to be referenced in their activity diagram and their data model. The data model section is particularly good as it explicitly spells out their protocol. If your game has networking, this is the document to emulate.

Family Style

A viral success (with 2+ million downloads on all platforms), Family Style was the audience favorite at the 2019 Showcase. This game is another example of networking, though they build on top of Firebase rather than using the (modern) CUGL networking API. With that said, unlike No Screws Attached, the CRC tables in this document are not great (and we have left many of our comments in this document).

Pig Life Crisis

Pig Life Crisis was the most polished mobile game at the 2019 Showcase. They really used scene graphs effectively and had some incredible animations. In addition, their activity diagram is one of the best done in this class. They had just the right level of detail – not too much or too little.


Underhand is the Reigns-inspired game from 2017 was another game that went viral on Reddit and received over 1 million downloads on Android. They were also one of the first CUGL games in this course (before 2017 we used various other engines). This document showed the early promise of CUGL as the dependency diagram is very clean and the rest of the document is very clear.


Discarded is a dungeon crawler using card mechanics that was developed in the 2018 class. Because of their card mechanics, they have a constraint system for determining when certain events are satisfied. This is an interesting architecture to look at, and the document does a good job of describing it.

Over the Arctic Hill

The 2014 game Over the Arctic Hills continues to be a great source of examples for this course. This document covers all of the requirements that we listed above and presents everything with the right amount of detail. None of its sections stand out as the best that we have ever seen, but it is one of the best “complete packages” that we have. This is the type of document that you should emulate.

Squeak & Swipe

As with previous documents, Squeak & Swipe continues to be an example of good documentation. Everything is clean and easy to read. Other than putting the dependency diagram later, this is a good model to follow. This document is also notable because they are using Tiled as their level editor, and this puts some contraints on the serialization model.


Beam was the winner of the Most Polished Game in the mobile division at the 2014 Showcase. Like Over the Arctic Hills, it is an example of a solid, complete document with no serious flaws. In fact, the only issue with this document is that the team does not vary the font size of the section headers enough, so that sections start to blur together.

Exodus Protocol

The specification for the 2013 strategy game Exodus Protocol is one of the best examples of data representation that we have seen in this class. It goes into detail about the tags, instead of just providing and example that we have to decode. On the other hand, it does not overwhelm us with tags, only focusing on the most important ones. Finally, note that this is a game from the introductory course, so there is no restoration plan.


Due: Sat, Mar 11 at 11:59 PM

You should submit a PDF file called architecture.pdf containing all of the information above. We ask that the file be a PDF so that we can annotate it in order to return it to you with feedback for possible revision. It is fine if you create the document in a program like Microsoft Word, but you should convert it to PDF before submission.

As the prospect of revision implies, this is not the final draft of your specification. You will have later opportunities to revise your concept. However, as with previous revisable documents, you should take this assignment seriously.