I’m putting together a list of the various types of API we might encounter. This is primarily a resource for technical writers, who may need to know what type of thing they could be asked to document if they take on the role of API tech writer.
A Google search didn’t reveal much material about API types. The best source of information is the Wikipedia page on APIs.
I tried searching for “API classification” and received plenty of information about engine oil. :D
So here goes… my attempt at an API classification.
Update: Content now available in a slide deck too
3 May 2014: I’ve created a slide deck which summarises the information in this post and includes some information from the comments on the post and from discussions with other tech writers. The slide deck is available on SlideShare:
Before we start: What is an API?
API stands for “application programming interface”. Put briefly, an API consists of a set of rules describing how one application can interact with another, and the mechanisms that allow such interaction to happen.
What is an interaction between two applications? Typically, an interaction occurs when one application would like to access the data held by another application, or send data to that app. Another interaction might be when one application wants to request a service from another.
A key thing to note: An API is (usually) not a user interface. It provides software-to-software interaction, not user interactions. Sometimes, though, an API may provide a user interface widget, which an app can grab and display.
There are two primary benefits that an API brings:
- Simplification, by providing a layer that hides complexity.
- Microsoft Word asks the active printer to return its status. Microsoft Word does not care what kind of printer is available. The API worries about that.
- Bloggers on WordPress can embed their Twitter stream into their blog’s sidebar. WordPress uses the Twitter API to enable this.
Web service APIs
A web service is a piece of software, or a system, that provides access to its services via an address on the World Wide Web. This address is known as a URI, or URL. The key point is that the web service offers its information in a format that other applications can “understand”, or parse.
A web service uses HTTP to exchange information. (Or HTTPS, which is an encrypted version of HTTP.)
When an application, the “client”, wants to communicate with the web service, the application sends an HTTP request. The web service then sends an HTTP response.
In the request, much of the required information is passed in the URL itself, as paths in the URL and/or as URL parameters.
In addition to the URL, HTTP requests and responses will include information in the header and the body of the message. Request and response “headers” include various types of metadata, such as the browser being used, the content type, language (human, not software), and more.
The body includes additional data in the request or response. Common data formats are XML and JSON. The process of converting data from internal format (for example, a database or a class) to the transferrable format is called “data serialization”.
Most often-used types of web service:
SOAP (Simple Object Access Protocol)
SOAP is a protocol that defines the communication method, and the structure of the messages. The data transfer format is XML.
A SOAP service publishes a definition of its interface in a machine-readable document, using WSDL – Web Services Definition Language.
XML-RPC is an older protocol than SOAP. It uses a specific XML format for data transfer, whereas SOAP allows a proprietary XML format. An XML-RPC call tends to be much simpler, and to use less bandwidth, than a SOAP call. (SOAP is known to be “verbose”.) SOAP and XML-RPC have different levels of support in various libraries. There’s good information in this Stack Overflow thread.
JSON-RPC is similar to XML-RPC, but uses JSON instead of XML for data transfer.
REST (Representational state transfer)
REST is not a protocol, but rather a set of architectural principles. The thing that differentiates a REST service from other web services is its architecture. Some of the characteristics required of a REST service include simplicity of interfaces, identification of resources within the request, and the ability to manipulate the resources via the interface. There are a number of other, more fundamental architectural requirements too.
Looked at from the point of view of a client application, REST services tend to offer an easy-to-parse URL structure, consisting primarily of nouns that reflect the logical, hierarchical categories of the data on offer.
For example, let’s say you need to get a list of trees from an API at example-tree-service.com. You might submit a request like this:
Perhaps you already know the scientific name of a tree family, Leptospermum, and you need to know the common name. You request might look like this:
The tree service might then send a response containing a bunch of information about the Leptospermum family, including a field “common-name” containing the value “teatrees”.
An example of a REST API: The JIRA REST APIs from Atlassian.
The most commonly-used data format is JSON or XML. Often the service will offer a choice, and the client can request one or the other by including “json” or “xml” in the URL path or in a URL parameter.
A REST service may publish a WADL document describing the resources it has available, and the methods it will accept to access those resources. WADL stands for Web Application Description Language. It’s an XML format that provides a machine-processable description of an HTTP-based Web applications. If there’s no WADL document available, developers rely on documentation to tell them what resources and methods are available. Most web services still rely on documentation rather than a machine-readable description of their interface.
In a well-defined REST service, there is no tight coupling between the REST interface and the underlying architecture of the service. This is often cited as the main advantage of REST over RPC (Remote Procedure Call) architectures. Clients calling the service are not dependent on the underlying method names or data structures of the service. Instead, the REST interfaces merely represent the logical resources and functionality available. The structure of the data in the message is independent of the service’s data structure. The message contains a representation of the data. Changes to the underlying service must not break the clients.
To use this type of API, an application will reference or import a library of code or of binary functions, and use the functions/routines from that library to perform actions and exchange information.
TWAIN is an API and communications protocol for scanners and cameras. For example, when you buy an HP scanner you will also get a TWAIN software library, written to comply with the TWAIN standard which supports multiple device types. Applications will use TWAIN to talk to your scanner.
The Oracle Call Interface (OCI) consists of a set of C-language software APIs which provide an interface to the Oracle database.
Class-based APIs (object oriented) – a special type of library-based API
These APIs provide data and functionality organised around classes, as defined in object-oriented languages. Each class offers a discrete set of information and associated behaviours, often corresponding to a human understanding of a concept.
The Java programming community offers a number of good examples of object oriented, or classed-based, APIs. For example:
- The Java API itself. This is a set of classes that come along with the Java development environment (JDK) and which are indispensable if you’re going to program in Java. The Java language includes the basic syntax and primitive types. The classes in the Java API provide everything else – things like strings, arrays, the renowned Object, and much much more.
- The Android API.
- The Google Maps Android API.
Functions or routines in an OS
Operating systems, like Windows and UNIX, provide many functions and routines that we use every day without thinking about it. These OSes offer an API too, so that software programs can interact with the OS.
Examples of functionality provided by the API: Access to the file system, printing documents, displaying the content of a file on the console, error notifications, access to the user interface provided by the OS.
Object remoting APIs
These APIs use a remoting protocol, such as CORBA – Common Object Request Broker Architecture. Such an API works by implementing local proxy objects to represent the remote objects, and interacting with the local object. The same interaction is then duplicated on the remote object, via the protocol.
As far as I can tell, most of these APIs are now considered legacy. Another example is .NET Remoting.
Hardware APIs are for manipulating addressable pieces of hardware on a device – things like video acceleration, hard disk drives, PCI buses.
Other developer products
There’s more to life than APIs, of course. :) A technical writer may be called upon to document other developer-focused products:
- SDKs – software development kits, which typically contain a set of tools that developers use to interact with, and develop on top of, your product.
- IDE plugins – custom additions to standard development environments, which give developers the extra tools they need to interact with your product from within a development environment like Eclipse, IntelliJ IDEA, or Visual Studio.
- Code libraries that developers can import into their projects.
- Other frameworks that support software development in a specific environment, such as custom XML specifications, templates, UI guidelines.
There’s more than one way to can has a cat
Your turn. What have I missed, and are there more useful ways of classifying APIs?
I’m curious to see how things have changed since I last asked this question, back in March 2012: What’s your favourite API documentation, and why?
Part of the reason for asking is that I’ll soon present a session at STC Summit 2014 on API technical writing. I want to give examples of excellent documentation. I have some favourite documentation sets myself, but it’s great to get the opinions of developers and other technical writers too.
So, have at it! :) Please comment on this post.
What’s your favourite API documentation, and why?
I’ll also collect any suggestions that people send via Twitter, Google+, and other channels, and add the links to this post.
OT: This has to be the world’s best bird. Well, it’s my current favourite anyway. This is a Tawny Frogmouth, spotted on an early morning walk. Tawny Frogmouths are night birds, about the size of a large owl (34-52 centimetres). During the day, they pretend to be old tree branches.
I’ll be speaking about API technical writing at STC Summit 2014. Part of the presentation is about useful tools for API technical writers. Since there are already some great resources on the Web about editors and IDEs, I plan to focus on a motley collection of “other” tools. Those that do a specific job very well. Those of which you’d say, “When I need it, I really need it.”
There are plenty of blog posts and articles about tools for documentation and code, including open source tools. Particularly when talking about editors and IDEs (Integrated Development Environments) most people have their favourites. The debates about which tool is best can get quite fiery!
Here are some useful links:
- Mike McCallister’s presentation, Open Source Tools for User Assistance. It’s well worth following Mike’s blog too.
- Chantel Brathwaite, writing on the TechWhirl blog about Technical Writing on a Shoestring.
- From Bret McGowen on the Rackspace blog, My Text Editor Final Four.
So, aren’t you going to talk about editors at all? ;)
My favourite IDE is Eclipse. I like to dabble in Android Studio and IntelliJ IDEA, just to see what’s happening.
Now that’s out of the way, let’s look at some super-useful and less-talked-about tools for API tech writers in particular.
Syntax highlighter for code samples
I frequently need to add a code sample to an HTML page, or include a slice of code in a presentation. Code is much easier to understand if the text is highlighted to indicate method names, variable declarations, and other syntactical essentials. And it just looks prettier too.
hilite.me converts a code snippet into styled HTML, which you can copy and paste into your page. Paste in your code, and select the coding language, to get the appropriate highlighting. Then click “Highlight!” to see the result. You can grab the HTML and CSS code, or copy and paste the highlighted text itself. You can even choose from a number of styles, such as “colorful”, “friendly”, “fruity”, and so on.
For example, I pasted in a Java “hello world” class, and asked for “tango” style highlighting. The “Preview” box at the bottom of this screenshot shows the result:
Testing web services and REST APIs
There’s an add-on for Chrome browser, called the Advanced REST Client, which I find very useful for getting examples of web service requests and responses. You can craft an HTTP request, then submit the request and see the response. This is a nice GUI alternative to a command-line tool like cURL.
Let’s say I want to use the Google Geocoding API to get a human-readable address for a pair of latitude/longitude coordinates. My URL would look like this:
I’ve pasted the above URL into the Advanced REST Client tab in Chrome, then used the add-on to expand the URL parameters, making it easy to see the composition of the HTTP request:
Now press the “Send” button to see the response. This is a partial screenshot:
Very handy indeed.
Chrome Developer Tools
The Chrome Developer Tools are a little tricky to grok, but once you’ve figured out what’s going on, they’re coolth personified. To find them, click the three-barred icon at top right of the Chrome window (the tooltip says “Customize and control Google Chrome”) then choose “Tools” > “Developer Tools”. The keyboard shortcut is Ctrl+Shift+I or Cmd+Shift+I.
A panel opens at the bottom of the page. It’s pretty busy, so take your time getting used to it. You can click an option to undock the panel and see it as a separate window, if you prefer that. In this screenshot, the DevTools panel is open at the bottom of the screen, and is showing the “Elements” tab:
There are many many things you can do with the DevTools. The Chrome DevTools documentation is a good guide. These are the functions I use most often:
- Check which CSS style is in effect on a particular block of HTML. This is particularly useful when there are a number of stylesheets at play. Sometimes the cascading effect of CSS doesn’t seem to follow the laws of gravity!
- Watch the error messages scrolling past on the “Console” tab. :)
- Edit HTML on the spot, to see the effect live on a web page before putting my changes into the source code.
Open Device Labs – Access to real devices and platforms for test-driving an app
It can be very difficult to try out an application on every supported device or platform. Especially for those of us dealing with mobile apps, there are just way too many devices out there for it to be feasible to have an example of each one.
One solution is to use emulators. But here’s an exciting initiative that I heard about recently: Open Device Labs.
The idea is that people may have last year’s mobile phone lying around, that they’d be willing to allow other people to use for testing. Some people may even want to donate new devices to the cause. Smart, enthusiastic people have set up hubs of Internet-connected devices at various locations around the world, and made them available to us all to use. For free!
I haven’t yet used a device from one of these labs, but the idea is awesome. What a great way to test an app, get screenshots, figure out the “how to” instructions you need to write, and just see how the user experience feels.
Mobile emulator in Chrome browser
With Chrome’s mobile emulation, you can make your desktop browser pretend that it’s something else. It can masquerade as an iPhone, Kindle, Blackberry, Nexus, and more. This is very useful for taking screenshots, and for seeing how responsive an app is to different device sizes and resolutions. The emulator is available via a fairly obscure setting in the Chrome Developer Tools panel.
Online source repositories are good for sharing code. In a tutorial, it works well to include code snippets and point readers to the complete source in a repo. Bitbucket and GitHub are very popular. I have accounts on both, because I’ve worked with teams on both. GitHub works with Git, while Bitbucket supports both Git and Mercurial.
That’s my list so far. If I find any more tools before the STC Summit in May, I’ll add them to the list I’m creating for my presentation. It will be fun to share them with the tech writers at the conference. Can you think of any super-useful tools to add to the list?
Technical writers often need to create sample code, to illustrate the primary use case of an API or developer tool, and to help developers get started quickly in the use of the API or tool. Here are some tips on how to go about creating that code. I’ve jotted down everything I can think of. If you have more tips to add, please do. :)
I recently published a set of documentation on a utility library created by Chris Broadfoot, a Google developer programs engineer. The utility library is an adjunct to the Google Maps Android API. The documentation includes an overview of all the utilities in the library, a setup guide, and an in-depth guide to one of the utilities. (I’ll document more of the utilities as time goes on.) As part of the guide to the marker clustering utility, I created some sample code that illustrates the most basic usage of the utility and gets developers up and running fast.
Quick introduction to the API and the utility library
The Google Maps Android API is for developers who want to add a map to their Android apps. The API draws its data from the Google Maps database, handles the displaying of the map, and responds to gestures made by the user, such as zooming in and out of the map. You can also call API methods to add markers, rectangles and other polygons, segmented lines (called polylines), images (called ground overlays) and replacement map tiles (called tile overlays). It’s all in the API documentation.
The utility library is an extra set of code that developers can include in their Android apps. It includes a number of useful features that extend the base API. One of those features is “marker clustering”. The full list of features is in the utility library documentation.
The marker clustering utility
The sample code illustrates the marker clustering utility in Chris’s utility library. So before diving into the code, you be asking:
What’s “marker clustering”?
Let’s assume you have a map with a large number of markers. (Typically on a Google Map, a marker is one of those orange pointy droplets that marks a place on the map.) If you display all the markers at once and individually, the map looks ugly and is hard to grok, especially when the map is zoomed out and many markers are concentrated in a small area. One solution is to group neighbouring markers together into a single marker icon (a “cluster”) and then split them into individual marker icons when the user zooms out or clicks on the cluster icon. That’s what Chris‘s marker clustering utility does.
What does marker clustering look like? See the screenshots in the documentation.
Developers can implement the classes Chris has created and customise the appearance and behaviour of the clusters. The utility library also includes a demo app, containing sample implementations of the utilities.
The sample code
The best way to describe a code library is to provide sample code. I created a simple marker clustering example, based on the demo app. Take a look at the sample code in the documentation section on adding a simple marker clusterer.
Now compare it to the code in the demo app that’s part of the utility library: ClusteringDemoActivity.java
The differences, in a nutshell:
- The sample code doesn’t show any of the “plumbing”, such as the library import statements.
- The sample code does include a listing of both the primary method that does the clustering (called “
setUpClusterer()“) and a class that’s important for developers to understand (“
public class MyItem implements ClusterItem“).
- Instead of reading input from a file, the sample code includes a method called “
addItems()” to set up some sample data directly from within the code.
- I’ve added plentiful comments to the sample code, explaining the bits that are specific to marker clustering or the sample itself.
In summary, the sample code provides all the developer needs to get a simple marker clusterer working, just by copying and pasting the code into an existing Android project.
How to write sample code
While writing the sample code, a thought struck me:
Hey, it’s actually quite an interesting process writing sample code. I’ll blog about what I’m doing here, and see what other technical writers have to say about it. :)
First, a stab at defining the goals for the sample code:
- Get the developer up and running as quickly as possible.
- Be suitable for copying and pasting.
- Work (do what it’s meant to do) when dropped into a development project.
- Be as simple as clear as possible.
- Provide information that is not easy to find by reading the code.
- Illustrate the primary, basic use case of the API or tool.
And here are my jottings on how to go about creating a useful code sample:
- Find out what the primary and simplest use case is. That is what your code should illustrate. Talk to the engineers and product managers, read the requirements or design document, read the code comments.
- Find out what you can safely assume about your audience. Can you assume they are familiar with the technology you’re working with (in my case, Java and Android development)? Do you know which development tools they are using?
- Find some “real” code that does something similar to what you need. Perhaps a similar function or a working implementation that’s too complex for your needs.
- Simplify it. Make names more meaningful. Remove functionality that’s unique to your environment or that adds super-duper but superfluous features. Remove plumbing such as import statements and all but the essential error handling.
- Put your into a framework and test it. The framework should be one that your audience will be using. In my case, that’s an Android development project.
- Take screenshots of the code in action. They’re often useful to give people an idea of the goal of the sample code, and of what the API or tool can do.
- Get the code reviewed.
- Include it in the doc.
- If possible, put the code in a source repository and hook it up to some automated tests, to help ensure it will remain current.
- As far as possible, have all the necessary code in one piece, so that people can copy and paste easily. This may mean moving stuff around.
- Add code comments. Engineers often add technical comments to the code, but don’t include an introduction or conceptual overview of what’s going on. And our target audience, developers, will often read code comments where they don’t read other docs. So code comments are a great medium for technical communication!
Perhaps the most important thing to do is to see yourself as the advocate for or representative of those developers who need to use the API or tool you’re illustrating. Think what questions they would ask if they had access to the people and tools that you do, and put the answers into the documentation and sample code.
To do this job, tech writers need a certain level of coding knowledge, and also a good understanding of what a developer needs to get started. The sample code provides a stepping stone between the conceptual overviews and the complex implementations.
Well, that’s all I can think of. What have I forgotten? :)
Here’s a tip that technical writers will love! You can start a YouTube video at a specific point, by including the time-from-start in the URL or as a parameter in an embedded video.
Let’s say the sales team has produced a video introducing a number of new features in your product. Or an engineer has covered a suite of classes in an API. As a technical writer, you are writing about just one of those features, or just a subset of the classes. So, you need to start the video at the right point. Otherwise you’ll lose your readers!
In the examples below, I’ve used an excellent video from Chris Broadfoot, a Google engineer who is showing developers how to add spiffy map features to their Android apps using the Google Maps Android API utility library. I’m currently writing the documentation which focuses on just one of the utilities Chris covers: the Bubble Icon Factory. Does that sound like fun? It is! Watch the video to see what it’s about. :)
Using a URL to start a YouTube video at a specific point
Add the ‘t‘ parameter with a value in minutes and seconds. For example, this YouTube URL starts the video one and a half minutes into the story, where Chris talks about bubble icons:
Starting an embedded YouTube video at a specific point
Use the ‘start‘ parameter and specify the number of seconds from the start of the video.
This is the code to embed a video using an iFrame, and start it at the 90-second point. Please assume the following code is within an HTML iframe element:
width="560" height="315" src="//www.youtube.com/embed/nb2X9IjjZpM?start=90" frameborder="0" allowfullscreen
Because this blog is on WordPress, I’ve used a WordPress macro to embed a video on this page and start it at the 90-second point. This is the code:
And here’s the result:
The YouTube documentation has a list of other useful parameters, including ‘end‘ for stopping the video at a given time, and ‘rel‘ for showing or suppressing the list of related videos when yours stops playing.