Amazon Simple Queue Service (Amazon SQS) is a message-oriented middleware in the cloud using software as a service model. It aims to eliminate the traditional overhead associated with operating in-house messaging infrastructures by providing reduced costs, simplified access to messaging resources, scalability and reliability. In order to provide those benefits Amazon SQS leverages cloud resources such as storage, network, memory, processing capacity. Using virtually unlimited cloud computing resources, an Amazon SQS provides an internet scale messaging platform. This paper presents benefits and examples of Amazon SQS programming interface developed in Actionscript 3.0 object-oriented programming language. This interface was developed to enable Adobe Flex mobile developers to facilitate integration efforts within organizations and between them using mobile devices (tablets and smartphones).

1. REST-style Actionscript programming interface
for message distribution using Amazon Simple
Queue Service
K. Popovic, Z. Hocenski
Siemens d.d. / Communications, Media and Technology, Osijek, Croatia
Faculty of Electrical Engineering / Institute of Automation and Process Computing, Osijek, Croatia
kresimir.popovic@siemens.com
Abstract - Amazon Simple Queue Service (Amazon SQS) is counterpart. In this model organizations are only
a message-oriented middleware in the cloud using software responsible for deploying the portion of the applications
as a service model. It aims to eliminate the traditional that interact with the web services and message queues.
overhead associated with operating in-house messaging
infrastructures by providing reduced costs, simplified access Message and data exchange are an essential aspect of
to messaging resources, scalability and reliability. In order any enterprise mobile application [3]. The ability to
to provide those benefits Amazon SQS leverages cloud exchange messages or consume data from on-premise or
resources such as storage, network, memory, processing cloud environments in a mobile device is, arguably, the
capacity. Using virtually unlimited cloud computing most relevant element of an enterprise mobility platform.
resources, an Amazon SQS provides an internet scale The key is to build components that do not have tight
messaging platform. This paper presents benefits and dependencies on each other, so that if one component
examples of Amazon SQS programming interface developed were to die (fail), sleep (not respond) or remain busy
in Actionscript 3.0 object-oriented programming language. (slow to respond) for some reason, the other components
This interface was developed to enable Adobe Flex mobile in the system are built so as to continue to work as if no
developers to facilitate integration efforts within failure is happening. In essence, loose coupling isolates
organizations and between them using mobile devices the various layers and components so that each component
(tablets and smartphones). interacts asynchronously with the others and treats them
as a black box. Loosely coupled system can be build
I. INTRODUCTION using messaging queues. If a queue is used to connect any
two components together, it can provide concurrency,
Mobile computing has drastically impacted the social high availability and mitigate load spikes.
and commercial aspects of our society [1]. Seeing the
explosion of mobile applications in the consumer world, Today, technologies such as Amazon SQS [4],
companies can't avoid dreaming about revolutionizing CloudMQ [5], Linxter [6], Microsoft Azure Message
their businesses with the presence of mobile applications. Queue [7] and others offer simple cloud-based messaging
The ability of extending business capabilities to mobile services to broker the communication between different
devices (tablets and smartphones) leads the priority list of endpoints. In this paper benefits and examples of Amazon
most CIOs (Chief Information Officer) [2]. However, the SQS programming interface developed in Actionscript 3.0
path to enterprise mobility goes beyond building sporadic object-oriented programming language (library name:
applications for a specific line of business systems. as3awsSDK.swc) are presented [8]. Interface is developed
Companies embarking on the enterprise mobility journey as publicly available Community Contributed Software
need cohesive strategies for important mobile for thin clients [9].
infrastructure aspects such as device management,
The goal of this paper is to present developed Amazon
identity, security, and monitoring, that are required to
SQS programming application interface for Actionscript
provide a true enterprise mobility experience. During the
3.0 and its benefits for Flex developer community.
last few years, cloud infrastructures have pushed the
frontiers of software development to areas never before The paper is organized as follows: Section II lists
imagined. In the context of enterprise mobility, the cloud recent available software development kits from
model and services present a unique model to simplify the prominent cloud providers and open-source community.
challenges of the traditional enterprise mobility model and Also benefits of Amazon Simple Queue Service (Amazon
to open new possibilities in the space. Conceptually, an SQS) are considered, and mobile application portability
enterprise cloud mobility platform removes the issue solution is recommended. Section III presents
complexities of the mobile enterprise server from the architecture of Amazon SQS API for Actionscript 3.0 and
corporate network by placing it in a cloud infrastructure one use case sample how it can be used in practice.
where it can leverage various cloud services to enable its
native capabilities. A cloud enterprise mobility
infrastructure represents a higher simpler model from the
infrastructure standpoint than its on-premise

2. II. RELATED WORK III. AMAZON SQS APPLICATION PROGRAMMING
As of recent, software development kits available INTERFACE FOR ACTIONSCRIPT 3.0
from prominent cloud providers and open-source Amazon SQS is used as message-passing mechanism
community provide APIs (libraries) that hide much of the between components. It acts as glue that holds together
lower-level complexity, including authentication, request different functional components. This not only helps in
retries, and error handling. They take the complexity out making the different components loosely coupled, but
of coding directly against a web service interface. TABLE also helps in building a more failure resilient system
I shows available software development kits from overall. If one component is receiving and processing
different cloud providers. requests faster than other components (an unbalanced
producer consumer situation), buffering will help make
the overall system more resilient to bursts of traffic (or
TABLE I. SOFTWARE DEVELOPMENT KITS
load). Amazon SQS acts as a transient buffer between
Software Cloud provider two or more components (controllers). If a message is
Development sent directly to a component, the receiver will need to
Kit Microsoft Linxter CloudMQ Amazon
consume it at a rate dictated by the sender. For example,
Home computer if the system was slow or if the launch time of the cluster
was more than expected, the overall system would slow
Java
down, as it would just have to wait. With message
queues, sender and receiver are decoupled and the queue
.NET
service smoothens out any “spiky” message traffic. These
service benefits can be used by mobile devices in an
PHP
innovative, simple and transparent way.
Ruby
A. Characteristics of a good API
Mobile What are characteristics of a good application
programming interface (API)? Answer to this question
iOS
has to be known to software developers before API
implementation.
Android
 Easy to learn (steeper learning curve) - an easy-to-
BlackBerry learn API features, consistent naming conventions
and patterns, economy of concepts, and
predictability. It uses the same name for the same
Each provider provides several publicly available concept, and different names for different
libraries for different development environments. For concepts. A minimal API is easy to memorize
proper use developer needs to have technical knowledge because there is little to remember. A consistent
about the environment in which he/she develops. This can API is easy to memorize because you can reapply
be time consuming and costly because e.g. for mobile what you learned in one part of the API when
development it is necessary to have iOS, BlackBerry and using a different part. The semantics should be
Android knowledge. Also, the same application needs to simple and clear, and follow the principle of least
be developed three times. Solution to the portability issue surprise.
is to use technology which enables developers to write  Hard to misuse - A well-designed API makes it
code once, and run anywhere. This is possible since June, easier to write correct code than incorrect code,
2011 using Adobe Flex SDK (version 4.5 or later) and encourages good programming practices. It
framework [10]. Flex is a highly productive, open source does not needlessly force the user to call methods
framework for building and maintaining expressive web in a strict order or to be aware of implicit side
applications that deploy consistently on all major effects or semantic oddities.
browsers, desktops and operating systems. This means
that source code written in Actionscript 3.0 can be also  Easy to read and maintain code that uses it -
compiled for all mobile devices. Knowing that, it was readable code can be concise or verbose. Either
prudent to develop an Actionscript 3.0 library for one of way, it is always at the right level of abstraction—
cloud providers which offer message queue service. neither hiding important things nor forcing the
Purpose of this library is to enable Adobe Flex developers software developer to specify irrelevant
to facilitate integration efforts within organizations and information.
between them using mobile devices. The benefit of doing
it this way has impact on application maintenance costs.  Easy to extend - Libraries grow over time. New
Amazon SQS owned by Amazon Inc. was chosen as classes appear. Existing classes get new methods,
message middleware because of proven maturity when methods get new parameters, and enums get new
compared to others and due to Amazon’s vast cloud enum values. APIs should be designed with this in
market share. mind. The larger the API, the more likely the
clashes between the new concepts and the existing
concepts. In addition, binary compatibility

3. concerns must be taken into consideration during  deleteMessage - remove a previously received
the original design phase. message from a specified queue.
Guidance above was taken as main beacon toward  deleteMessageBatch - remove multiple previously
good API during the design and development phase of received messages from a specified queue.
Amazon SQS API for Actionscript 3.0. After
development phase it was shown that developers  setQueueAttributes - control queue settings like
should strive for minimalism and consistency, but only the amount of time that messages are locked after
to the extent that they contribute to meeting the criteria being read so they cannot be read again.
listed above. Consistency coincides broadly with  getQueueAttributes - get information about a
conceptual integrity, the principle that a complex queue like the number of messages in it.
system should have a coherent design, reflecting the
vision of one architect.  getQueueUrl - get the queue URL.
Quote from F.P. Brooks [11]: „I contend that conceptual  addPermission - add queue sharing for another
integrity is the most important consideration in system AWS account for a specified queue.
design. It is better to have a system omit certain
 removePermission - remove an Amazon AWS
anomalous features and improvements, but to reflect one
account from queue sharing for a specified queue.
set of design ideas, than to have one that contains many
good but independent and uncoordinated ideas.“  releaseResources – this is a special function which
removes all event listeners and releases any
B. Architecture of developed Amazon SQS API for resources that might be held open on client side.
Actionscript 3.0 – as3awsSDK.swc Execution of this method minimizes memory
Amazon SQS library for Actionscript 3.0 consumption.
as3awsSDK.swc is consisted of three basic model types:
event model, interface model and class model. Interface Class model contains two core classes:
model employs a simple interface  com.amazonaws.AmazonWebServiceClient –
com.amazonaws.services.sqs.AmazonSQS (defined in abstract class which performs data stream
Amazon SQS WSDL version 2011-10-01) that is easy to encoding using createURLRequest protected
use and extend (see Figure 1). function. It is designed as a base class which can
be reused by other Amazon AWS services, e.g.
Amazon Cloudwatch monitoring service [12],
DynamoDB noSQL database [13], etc.
 com.amazonaws.services.sqs.AmazonSQSClient
– queue client which contains implemented and
documented asynchronous queue service public
functions. Each function is unique and there is no
dependence between each other.
Event model uses interface
Figure 1. Basic architecture overview of Amazon SQS API for flash.events.IEventDispatcher. The IEventDispatcher
Actionscript 3.0 interface defines methods for adding or removing
event listeners, checks whether specific types of event
The following AmazonSQSClient requests defined by listeners are registered, and dispatches events. Event
interface AmazonSQS are provided: targets are an important part of the Flash® Player and
Adobe AIR event model. The event target serves as
 createQueue - create queues for use with your the focal point for how events flow through the display
Amazon AWS account. list hierarchy. When an HTTP/HTTPS COMPLETE
 listQueues - list your existing queues. event occurs, an event object is dispatched into the
event flow from the root of the display list. The event
 deleteQueue - delete one of your queues. object makes a round-trip journey to the event target,
which is conceptually divided into three phases: the
 sendMessage - add messages to a specified queue.
capture phase includes the journey from the root to the
 sendMessageBatch - add multiple messages to a last node before the event target's node; the target
specified queue. phase includes only the event target node; and the
bubbling phase includes any subsequent nodes
 receiveMessage - return one or more messages encountered on the return trip to the root of the display
from a specified queue. list.
 changeMessageVisibility - change the visibility HTTP(s) request responses in XML format are
timeout of previously received message. caught by an event model, parsed and deserialized to
 changeMessageVisibilityBatch - change the Actionscript 3.0 result object for easier user handling.
visibility timeout of multiple previously received During XML namespace parsing, response format and
messages.

4. mandatory parameters are checked if they are properly
formatted, if not exception will be thrown.
Usage of these three models guarantees consistency in
future Amazon SQS API library upgrades. This means
that Amazon SQS API can be used as a template for
creation of new services in the future.
C. How to use Amazon SQS API for Actionscript 3.0
For proper programmatic usage it is necessary to
understand that API only works in asynchronous
environment because it is based on Adobe Flash and Figure 3. Taxi reservation service
Adobe AIR technology. Every request (sendMessage
function, see Figure 2) has assigned two callback Use case description:
functions called when a specific event occurs.
 iPhone / Android / BlackBerry user opens
Taxi reservation mobile application.
 User enters his first name, last name, pickup
location, dropdown location, number of
people and a phone number.
 Reservation request is send towards Amazon
SQS queue TAXI_RESERVATION and
stored there until service consumer (e.g.
harvest server) pick it up.
 Harvest server checks every e.g. 30 seconds
TAXI_RESERVATION queue status and
harvests messages if there are any. When the
message is consumed from queue it needs to
be processed and stored into a database.
After the message is consumed it needs to be
deleted from the TAXI_RESERVATION
queue.
 If a user reservation request can be served
(taxi car is available) dispatcher will call the
user and confirm reservation or send an SMS
/ e-mail.
The advantage of working with queues is that if the
harvest server is offline reservation records can be
consumed later after harvest server comes back
Figure 2. Amazon SQS sendMessage sample for Actionscript 3.0 online. With this degree of independence, taxi software
components are protected from each other and can better
ResultHandler function is called when positive HTTP/ recover from component failure. If the SOA (Service
HTTPS response event occurs (result code 200 OK) and Oriented Architecture) is designed correctly, the failure
the faultHandler for negative event (result code >= 400). of a single component should not take down other
Other functions defined in interface components in the system and thus loose coupling creates
com.amazonaws.services.sqs.AmazonSQS are used in the architectures that are more resilient. Moreover, this also
similar way. This means that developers will have a steep lends itself better to creating a failover subsystem,
learning curve and become quite proficient in API usage moving from one instance of a component to another
with a minimum amount of effort/time. without affecting the other components in the SOA.
D. Taxi reservation service – usecase sample IV. CONLUSION
One of possible usage of mobile device and custom In this paper Amazon Simple Queue Service (Amazon
developed as3awsSDK.swc library is for connecting to SQS) programming application interface for Actionscript
Amazon SQS service to store taxi reservation messages 3.0 (as3awsSDK.swc) has been presented and its benefits
(see Figure 3). It can be quite useful when taxi dispatcher for Flex developer community. Most valuable advantage
phone lines are busy. The mobile application which does of programming application interface for Actionscript 3.0
reservation is portable to all mobile devices because it (compiled with Flex SDK compiler 4.5 or greater) from
must be compiled with Flex compiler for proper library technical point of view is portability. Code compiled with
usage. the Flex SDK compiler follows the slogan “write code
once, and run anywhere”. It enables developers to deploy

5. cloud message queue enabled mobile application on [7] Microsoft Azure Message Queue, Queue Service Rest API,
several different mobile OS result of which are reduced http://msdn.microsoft.com/en-
us/library/windowsazure/dd179363.aspx, February 05, 2012.
development costs and time. During the time of writing
[8] K. Popovic, Amazon SQS API library (version 1.4.1),
this paper library was downloaded by open source https://bitbucket.org/Kresimir/as3awssdk/overview, February 05,
community 176 times. 2012.
[9] Amazon Inc, Amazon AWS SDK library (actionscript 3.0),
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