**2. Architecture attributes and RFID technology**

Relying on the experience gained by analyzing existing RFID-based applications and by de‐ veloping RFID-based applications, we outline three architecture attributes among the attrib‐ utes presented in [1]: (i) functionality, (ii) scalability, and (iii) cost. For each attribute, we present its different aspects which are influenced by the use of RFID technology.

#### **2.1. Functionality attribute**

Functionality is the ability of the system to do the work for which it was intended.

All architectural patterns give the ability to read/write the avatar of a read tag.

A first aspect of the functionality attribute is to check how the application behaves when it queries the avatar of a read tag. Is it guaranteed that the returned avatar has indeed the val‐ ue which was last written? In other words, is there a staleness issue of avatar of a read tag?

The second aspect concerns the possibility of knowing the value (or having an order of idea of the value) of the avatar of a remote tag. By "remote", we mean that the user is not physi‐ cally near the tag: The user is not able to put her reader on the tag. All she has is the identifi‐ er of the remote tag.

The third aspect is the staleness issue of the avatar of a remote tag. If the user is able to know the avatar of a remote tag, is it guaranteed that the returned avatar has indeed the last values associated to the tag?

#### **2.2. Scalability attribute**

thoughts. In a survey about RFID in pervasive computing, [4] presents several application examples. Depending on the application, avatars are stored either in a central database or in the tags themselves. But the authors do not give any clues on why an application has chosen to store its avatars in a given location. On the other hand, [1] lists the attributes which must be accommodated in a system architecture. Above all, there are the functionalities which are required from the system. Then, orthogonal to these functionality attributes, there are quali‐ ty attributes. The authors distinguish system quality attributes (availability, modifiability, performance, scalability, security, testability, and usability), business qualities (time to mar‐ ket, cost and benefits, and projected lifetime), and qualities about the architecture itself (e.g.

So we have analyzed several existing industrial or experimental RFID-based applications. Moreover, we have developed RFID-based applications. From this experience, we identify the relevant attributes to compare RFID-based architectural patterns. We present them in section 2. With these identified attributes and their different aspects, we analyze four RFIDbased architectural patterns, used by applications to access the avatar of a tagged entity. In the *centralized architectural pattern*, the mobile device reads an identifier on the RFID tag; then it contacts a server which associates this identifier to the avatar stored in a central data‐ base or in a database distributed between several companies [2]. With the *semi-distributed ar‐ chitectural pattern*, each mobile device holds a local copy of a central database associating RFID identifiers to avatars [5]. In the *distributed architectural pattern*, each RFID tag holds the avatar [6]. With the *RFID-based Distributed Shared Memory*, RFID tags hold the avatar and a replica of the avatar of other tags [7]. Sections 3 to 6 detail all of these architectural patterns: they present application examples and analyze the architectural pattern with the attributes identified in section 2. Thanks to this analysis, in section 7, we are able to provide guidelines to choose the convenient RFID-based architectural pattern. Finally, section 8 concludes this

Relying on the experience gained by analyzing existing RFID-based applications and by de‐ veloping RFID-based applications, we outline three architecture attributes among the attrib‐ utes presented in [1]: (i) functionality, (ii) scalability, and (iii) cost. For each attribute, we

A first aspect of the functionality attribute is to check how the application behaves when it queries the avatar of a read tag. Is it guaranteed that the returned avatar has indeed the val‐ ue which was last written? In other words, is there a staleness issue of avatar of a read tag?

present its different aspects which are influenced by the use of RFID technology.

Functionality is the ability of the system to do the work for which it was intended.

All architectural patterns give the ability to read/write the avatar of a read tag.

conceptual integrity). But the authors do not focus on RFID specific features.

chapter and proposes perspectives for this work.

28 Radio Frequency Identification from System to Applications

**2.1. Functionality attribute**

**2. Architecture attributes and RFID technology**

The scalability criteria category evaluates how each architectural pattern behaves when there are numerous tags or numerous readers.

Its first aspect is the maximum number of tags which can be handled by the architectural pattern.

The second aspect characterizes the sensitivity of the architectural pattern to the number of simultaneous RFID tag read operations.

#### **2.3. Cost attribute**

The cost attribute groups all of the aspects which have an influence on the installation costs or the operational costs of the RFID-based application.

The first cost aspect concerns the requirement for a global network: do RFID readers have to be able to access at any time and any place to a specific computing machine (for instance, a server in the case of the centralized architectural pattern)? To fulfill this requirement, the readers may be equipped with a wired connection. In that case, the mobility of the readers is limited. The readers may also rely on Bluetooth® or Wi-Fi gateways. Both of these gateways may introduce installation costs. Moreover some readers may not be Wi-Fi enabled. For in‐ stance, the Nokia 6212 mobile phone is NFC-enabled, but has no Wi-Fi capabilities. Finally the reader may rely on a mobile data connection (e.g. UMTS, HSDPA, etc.). Such solution introduces operational costs because of data plans.

The second cost aspect concerns the RAM requirement on each tag. The more RAM there is on the tag, the more expensive the tag is. Notice that RAM may actually be prohibited on tags for technical reasons and not for cost reasons. For instance, application may require the use of low-frequency tags (e.g. 125 kHz), so that readers can interact with tags even though there is a liquid between tags and readers. In this case, the throughput is too low for a tag to host information other than its identifier.

The third cost aspect concerns the introduction of a new tag in the environment. For each architectural pattern, we determine the sequence of operations which is required in order to introduce a new tag in the environment. Knowing this sequence, we can determine how long this sequence lasts. Because this initialization procedure is executed by a human or a robot operator, its cost is proportional to the time spent.

The final cost aspect is related to the reinitialization of all of the tags. This criterion concerns only applications which, during their lifetime, need sometimes to have each tag given a new initial value. For instance, this is the case of Paris public transportation system. Users are equipped with a transportation pass containing an RFID tag. At the beginning of a month, each user has to reload her pass (to refresh her access rights): in other words, the tag has to be reinitialized. Some RFID-based games also require tag reinitialization. Indeed, in the case of non-permanent games, users play during successive game sessions. Thus at the beginning of each session, all of the tags must be reinitialized.

Next section gives examples of this architectural pattern.

tectural pattern, but without being compliant to EPCglobal.

Aspire RFID is an Open Source middleware which is compliant to the specifications of EPC‐

Choosing the Right RFID-Based Architectural Pattern

http://dx.doi.org/10.5772/54069

31

Next paragraphs present products or prototypes developed according to centralized archi‐

*PAC-LAN* is a game prototype in which players are equipped with NFC mobile phones without any GPS capabilities [9]. Players must interact with NFC tags which have been dis‐ seminated throughout a neighborhood. In a central database, the identifier of each tag is as‐ sociated to geographical coordinates. When a player reads a tag, her mobile phone uses the UMTS network to contact the server with the tag's identifier. The server queries its database, finds the geographical coordinates, and broadcasts them to all of the players. An administra‐ tive application is provided to reset a game on the server. Such reset has an impact on all of

[10] proposes an application so that visitors of an art exhibition can discover the paintings in another way. NFC tags are dispatched on the back of exposed paintings. Equipped with an NFC-enabled phone, the visitor puts her phone on spots of the paintings which intrigue her. Phone reads the identifier stored in the tag. Then, it contacts an uGASP server [11-12]. After consulting an internal database, this server indicates to the mobile phone what must be done: display a text, an image, or play an audio comment. Thus the author of the painting is

*Via Mineralia* is a pervasive serious game which goal is to enrich the visit of a Freiberg museum [13]. In this game, the visitor uses a PDA equipped with an RFID reader. RFID tags (holding a unique identifier) are dispatched in the showcases which the museum wants to emphasize. When the PDA scans a tag, it sends an HTTP request (with tag's identifier) to a web server. To do so, the PDA uses a Wi-Fi network which covers the whole museum. The server answers to the PDA with multimedia information. The PDA

*Touchatag* company (formerly Tikitag) sells NFC readers which can be connected to Win‐ dows or Mac-OS personal computers, and NFC tags dedicated to Touchatag [14]. A custom‐ er can then connect to http://www.touchatag.com web site, and define the reaction to be associated to the reading of one tag. When the NFC reader reads a tag, it contacts the Tou‐ chatag application which runs permanently on customer's personal computer. Then, via the Internet network to which the computer is connected, this application contacts a Touchatag service called *Application Correlation Service* (ACS). Touchatag application gives tag's identi‐ fier to ACS. Then, ACS queries Touchatag database to find reaction associated to the reading of this tag. It sends back this information to Touchatag application. The touchatag applica‐ tion reacts in the appropriate way. For instance, let's assume that the customer has specified the following action on Touchatag web site: when tag *r* with identifier *i* is put on the reader, customer wants her browser to access to Uniform Resource Locator (URL) of a web site *w*.

global [8]. It proposes several examples of industrial applications for tracking goods.

**3.1. Examples**

the players' mobile phones.

able to communicate with the visitor.

displays them in a navigator.

In this section, we have defined different aspects of three architecture attributes: (i) function‐ ality, (ii) scalability, and (iii) cost. These aspects are influenced by the use of RFID technolo‐ gy. We use them to compare the behavior of four RFID-based architectural patterns. We start by analyzing centralized architectural pattern.
