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Overview of Xcode Design Tools

Xcode includes two separate design tools, with similar forms but different functions. Together, the tools allow you to model both the classes in your application and entities that represent your data. Although they are in some respects similar, class modeling and entity-relationship modeling are fundamentally different and serve different purposes—both are discussed below.

The two tools share some common functionality. They allow you to create models that form part of your project. They allow you to browse through the contents of the model using a set of table views and to visualize the contents in a diagram.

Control over how models are displayed is where Xcode differs from other design tools. Other IDEs that provide a graphic class browser typically give you little control over display—you see what it wants to show you. With Xcode, you have coarse-, medium-, and fine-grained control over what is displayed and how. You can edit the diagram in the same way you might in common graphics editors. For example, you can color, move, and align elements to arrange them how you wish; zoom in and out of the diagram; and choose whatever page and grid sizes you want. Moreover, your models never become stale.

In this section:

Class Modeling
Data Modeling
Why Are Modeling Tools Useful?

Class Modeling

Class modeling allows you to understand and explore the classes in your project, whether they’re written in Objective-C, C++, Java, or a mixture of those languages. You can get a bird’s eye view of your project structure, look at relationships among classes, or scan quickly through class member and method types, parameters, and return values. You can use class modeling to augment or replace the Xcode class browser. The class model is saved with your project (you can even commit it to your repository), so other team members can get an overview of your code structure from the class model.

You can use the tool to visualize and browse class hierarchies not only in terms of the class relationships (subclass and superclass), but also in terms of what protocols (or interfaces in Java) a class implements, and what categories are present. You can even add comments to call out notable things about specific classes.

Unlike most other modeling tools, you control the set of files (groups, targets, and so forth) that are modeled, the position and layout of the classes in the diagram, and even what classes are shown. Moreover the Xcode class information is always up to date. Class models always represent the actual classes in files, groups, and targets in your project, and are automatically updated as you change your source code—even if you add, remove, or refactor classes.

Data Modeling

The data modeling tool is like the class modeling tool in that you can, for example, lay out a diagram to represent your model visually, but different in that it deals with entities and the relationships between them, not with classes and hierarchies. There is not necessarily a 1:1 relationship between entities and classes—for example, the same class may be used to represent more than one entity. For more about data modeling, see [Modeling Document].

More importantly, however, you use the data modeling tool to define what is in effect a source file—a schema for Core Data. The data model ultimately becomes part of your build product and is used by your application at run time. Instances of entities are typically stored in a persistent store (typically a file).

Why Are Modeling Tools Useful?

There are a number of reasons why modeling tools are useful. Some reasons apply to both the class and data models, some apply to one or the other.

A graphical representation of your project gives you a better conceptual overview of your project than raw XML or a mass of source files . In particular, with Xcode, it gives you a developer’s eye view of your project, not a computer-generated representation . You can customize the view to see the information you need, not what the computer thinks is important or requires you to see . This is especially useful for communication between members of a team, or for homing in on a specific aspect of a project [see filtering]. In addition, the class modeling tool may also be useful for learning about functionality provided by existing libraries.

In terms of navigation, the browser view gives you an alternate means of navigating through your source, following relationships where appropriate. It provides a compact representation and summary of the classes or entities in your project, including their properties and behaviors, and (for the class browser) an easy way to get to relevant documentation.

Both class and data models are project resources. A class model is stored with the project as it is an integral part of development process . A data model is stored as part of the project because it is essential to Core Data—it is also included in a target as it is compiled for deployment .

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