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2009 | Buch

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Access to Mobile Services

verfasst von: Athman Bouguettaya, Xu Yang

Verlag: Springer US

Buchreihe : Advances in Database Systems

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

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Access to Mobile Services focuses on methods for accessing broadcast based M-services from multiple wireless channels. This book presents a novel infrastructure that provides a multi-channel broadcast framework for mobile users to effectively discover and access composite M-services. Multi-channel algorithms are proposed for efficiently accessing composite services.

Access to Mobile Services provides an in-depth survey of wireless data access and motivates the need to treat mobile services differently. A wireless adaptation of Service Oriented Architecture (SOA) is also covered.

Designed for researchers and practitioners who work in the general area of mobile services, this book is also suitable for advanced-level students in computer science.

Forewords by:
Michael P. Papazoglou, Tilburg University, The Netherlands
Fabio Casati, University of Trento, Italy

Inhaltsverzeichnis

Frontmatter

1. Introduction

The Internet was originally invented as a technology for sharing information among computers for scientific research purposes. Early standards, such as telnet protocol [45], Simple Mail Transfer Protocol (SMTP) [67], and File Transfer Protocol (FTP) [46], further improved the ability of exchanging information through the Internet. By the end of 1990s, with the development of HyperText Transfer Protocol (HTTP) [13] and other core Web technologies, the Internet has evolved to become the medium for connecting hundreds of millions of computers and exchanging massive amount of information. Given its great capacity and huge customer base, the Internet has provided companies with new business opportunities. As a result, more and more companies have changed their business models and started using the Internet as an important means of conducting their daily businesses. The Internet has now become a commonly used medium for business activities, which are often referred to as Electronic Commerce or E-commerce [38, 27].

Enabling technologies for E-commerce have been around for almost three decades. They provide businesses with means for interacting with their peers (B2B Ecommerce) and customers (B2C E-commerce). One of the early standards for fulfilling requirements of E-commerce is Electronic Data Interchange (EDI). EDI is a standard for the electronic exchange of information between entities using standard, machine-processable, structured data formats [6]. EDI has provided a means for different businesses to interact with each other. However, EDI requires applications to use standardized information. With great heterogeneity of the information on the Internet today, this becomes a severe limitation. A number of middleware technologies, such as CORBA, RMI, and EJB, have emerged since 1980s [42, 52, 51]. These technologies have provided new means for applications from different companies to communicate with each other over the networks. The great advantage of these technologies is that the communication details are transparent to users. Different business applications can interact with each other without having to worry about how the actual interaction takes place. However, all these middleware technologies require the interface between any two applications to be pre-defined. New interfaces would have to be built if a business entity wants its applications to interact with applications from different business partners. This greatly limits the usage of middleware technologies on the Internet, especially for businesses that require the interaction to be dynamic. By dynamic interaction, we mean any application can dynamically choose whom to interact with based on its best business interests. For example, assume a company that assembles and sells desktop computers has an automatic ordering system to order computer parts from different vendors and each vendor also has a automated system to process orders. To find out the lowest price of a computer part, the automatic ordering system would need to query each vendor to obtain the price. With the increasing number of vendors, the system would also need to automatically discover new vendors. Since the interfaces to different vendors’ systems could be different, the automatic ordering system would need to know how to interact with each vendor’s system. Apparently, traditional E-commerce technologies do not work efficiently with such business activities.1

Xu Yang, Athman Bouguettaya

2. Access to Broadcast M-services: Issues and Challenges

In this chapter, we discuss the need for new access methods and an accompanying infrastructure for broadcast based M-services. The infrastructure of traditional wireless broadcast systems cannot keep up with the rapid development of wireless technologies and the fast increasing wireless services. It is getting more difficult for mobile users to find suitable wireless services. Existing infrastructure also does not facilitate collaboration of multiple services. In this book, we discuss applying Web services technologies into wireless broadcast environments and propose a new Mservices infrastructure. One of the most important issues in broadcast environments is efficient access to broadcast information. A wide range of work has been done in the past two decades in studying efficient access in traditional data wireless broadcast systems. However, new access methods are needed due to the following new challenges for broadcast M-services systems:

Access pattern: Accessing M-services is a different process from accessing data and has a different access pattern.

Service dependencies: Services could have various dependencies between each other that could affect access efficiency.

Service-data dependencies: Each service could request for one or more data items. Access methods should consider the dependencies between services and their required data.

Access semantics: There are a few semantics that have impact on access efficiency and should be considered by access methods.

The focus of this book is to investigate efficient access methods for broadcast based M-services. The new access methods should address the challenges mentioned above.

Xu Yang, Athman Bouguettaya

3. Traditional Data Access Methods

Access efficiency has drawn a lot of research attention in the past few decades. Several wireless data access methods have been proposed to improve data access efficiency in wireless environment. These methods are evaluated in different environment contexts defined by the authors. Hence, it is difficult for readers to compare these methods because different environmental settings are used. To better analyze different access methods, we present a common analytical model for wireless environment. We define a set of commonly used environmental parameters that have impact on access efficiency.We selected a few most recognized access methods and derived analytical cost models for them. A testbed is developed to implement data access in wireless environment and simulate a wireless broadcast environment. The purpose of this testbed is to provide a platform to compare, evaluate, and help develop new access methods. The testbed supports several adjustable environmental settings for studying access methods under different settings. Extensive experiments have been conducted to compare the selected data access methods.

Xu Yang, Athman Bouguettaya

4. Adaptive Data Access Methods

In this chapter, we present an adaptive method we proposed to improve efficiency of wireless data access. The proposed method is based on the observation that the index tree based methods preserve good access time as well as stable overall performance and that the hashing method exhibits good tuning time. By combining these two techniques, the new method takes the advantages of both techniques. As a result, it exhibits greater flexibility and better performance.

As previously shown, the tuning time of hashing depends on Nc, which in turn depends on the number of collisions. The number of collisions normally depends on how good the hashing function is. Thus, deriving a good hashing function is crucial for good tuning time. However, because of the heterogeneity of broadcast data in different applications, this is usually difficult to achieve. Furthermore, the hashing function itself is included in every data bucket. This obviously increases the broadcast cycle, and thus, the access time. In our method, hashing is used only to partition the broadcast data into a number of partitions. B+ tree technique is then used to index each partition. The hashing function is only stored at the beginning of each partition. Since the number of partitions is a small number compared to the number of all data items, the overhead introduced is much smaller than that in hashing based method. We now show how hashing and index tree techniques are combined in our method:

First level hashing: Generate hashing value (h1) for key attribute of each data item using a hashing function H1. The hashing value generated at this step is similar to the hash value in simple hashing method.

Second level hashing: Use another hashing function (H2) to produce p second level hashing values (h2) based on the value of h1 generated in the first step. This process will partition the broadcast data into p parts. All data items having the same second level hashing value will be in the same partition.

Generating the index tree: Within each partition, generate an index tree on the key attributes of the data items in the partition.

Xu Yang, Athman Bouguettaya

5. Efficient Access to Simple M-services Using Traditional Methods

In this chapter, we discuss accessing simple M-services using traditional wireless access techniques. First, we show how different access methods can be applied to M-services environment. Then, we present analytical cost model for each access method.

As already mentioned, there are two important factors that are normally used to measure the performance of data access in wireless environments: Access Time and Tuning Time. Applying this concept to M-service environment, the access and tuning times reflect two important aspects of access to M-services, the response time and energy efficiency. In the context of M-services, we define access time and tuning time as follows:

Access Time: This is the total client waiting time, starting from the issuance of a service request till its completion.

Tuning Time: Tuning time is the time when CPU and/or wireless receiving devices are active, which means mobile clients are either actively processing requests and/or retrieving data from wireless channels. Tuning time includes the time to download or update the registry (if required), find and download the requested M-service, execute the M-service, and retrieve the requested data items.

Xu Yang, Athman Bouguettaya

6. Semantic Access to Composite M-services

In this chapter, we study how to efficiently access composite M-services in wireless broadcast systems. First, we present a novel wireless broadcast infrastructure that supports discovery and composition of M-services. Then we define access semantics for this infrastructure and study how to leverage these semantics to achieve best possible access efficiency.

Xu Yang, Athman Bouguettaya

7. Broadcast Channel Organization

A broadcast channel organization determines how information is organized in broadcast channels. Mobile devices must know the channel organization in order to find required information in a broadcast channel. The actual channel organization has direct impact on access efficiency because it determines how the broadcast information can be retrieved. The most straightforward channel organization is called “flat broadcast”, which is to directly broadcast data without providing any additional information on how to locate the broadcast data.With flat broadcast, mobile devices must stay active all the time to filter retrieved information in order to find requested data. This is obviously not efficient especially for mobile devices with limited power supply. In this chapter, we propose a few channel organizations suitable for the broadcast-based M-services infrastructure. For each channel organization, we also present access protocols for mobile devices to retrieve information from these channels.

Xu Yang, Athman Bouguettaya

8. Implementation and Practical Study

In this chapter, we provide practical study of the proposed infrastructure, access methods, and channel organizations. A testbed is implemented for simulating accessing composite services in a broadcast-based environment. First, we present the architecture of the testbed. Then we discuss the experiments that were conducted for studying the efficiency of the proposed access methods and channel organizations. In these experiments, we also study the impact of different semantics on the access efficiency.

Xu Yang, Athman Bouguettaya

9. Open Problems

In this book, we assume that supported composite services are pre-defined and can only contain simple services. This means all required services and their locations can be determined based on the BPEL and index information. In reality, however, composite services could be much more complex. For example, a composite service could invoke other composite services. This would result in a more complicated invocation sequence. Furthermore, only two types of BPEL activities, sequence and flow, are considered for composite services covered in this book. BPEL activities such as if, while, forEach, and repeatUntil ([68]) could produce more complex composite services than the supported types in this book. For example, an if activity indicates that some invoked services may not be determined until the invoking services have been executed. This would require access methods to update the access sequence based on which services are to be invoked. Some other BPEL activities such as while could require some services to be executed repeatedly. In such case, these services might need to be cached locally for a longer period of time to avoid frequent retrievals from broadcast channels.

Xu Yang, Athman Bouguettaya

Backmatter

Titel: Access to Mobile Services
verfasst von: Athman Bouguettaya
Xu Yang
Verlag: Springer US
Electronic ISBN: 978-0-387-88755-5
Print ISBN: 978-0-387-88754-8
DOI: https://doi.org/10.1007/978-0-387-88755-5

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Inhaltsverzeichnis

Frontmatter

1. Introduction

2. Access to Broadcast M-services: Issues and Challenges

3. Traditional Data Access Methods

4. Adaptive Data Access Methods

5. Efficient Access to Simple M-services Using Traditional Methods

6. Semantic Access to Composite M-services

7. Broadcast Channel Organization

8. Implementation and Practical Study

9. Open Problems

Backmatter

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