LNCS 4278 - Spatial Data Access Patterns in Semantic ... - Springer Link

Spatial Data Access Patterns in Semantic Grid Environment Vikram Sorathia and Anutosh Maitra Dhirubhai Ambani Institute of Information and Communication Technology (DA-IICT), Gandhinagar - 382 007, Gujarat, India {vikram sorathia, anutosh maitra}@daiict.ac.in http://www.daiict.ac.in

Abstract. Starting from the era of stove-piped Geographical Information Systems up to interesting mash-ups involving Internet based mapping services, the approaches of handling Geographical Information (GI) have changed significantly. This paper briefly concentrates up on the distinctive features and current implementations of Spatial Data Access Patterns. Considering the information requirements of the users in Emergency Operations Center, this paper identifies the issues and challenges in handling GI in dynamically changing environments. Two new patterns based on appropriate integration of Semantics and Grid technology are introduced, that may satisfy the identified requirements. Necessary alterations in current practices for handling GI is discussed with detail considerations for realization of these patterns on open environments.

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Introduction

The primary goal of GI Science is to provide right information to right person at right time[1] on a geo-spatial platform. The task involved in achieving this goal are: monitoring, representing, processing, handling and delivering the content to the user[2]. These tasks can be modified and executed in specific manners to match the user information requirements. Such distinctive approaches are identified and categorized as Spatial Data Access Patterns(SDAPs) to reveal the unique features, benefits and issues exhibited by them. As these methods were evolving to meet more complex user needs, the parallel developments in Semantic Web technology and Grid Computing environment also took place. These technologies introduced benefits of inter-organizational interoperability and non-trivial quality of service in dynamic environments. Current approaches to achieve the objectives of the GI Science is reconsidered in the light of novel application requirements. This paper mainly tries to explore how to exploit semantic grid environment using spatial information in order to change the way information needs are identified, collected, represented, processed, managed and published to meet organizational goals. R. Meersman, Z. Tari, P. Herrero et al. (Eds.): OTM Workshops 2006, LNCS 4278, pp. 1586–1595, 2006. c Springer-Verlag Berlin Heidelberg 2006 

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GI Access Patterns

Spatial Access Methods covered in literature provides detail overview of various methods at data structure and algorithm point of view. One can choose appropriate methods from the available pool of space-driven or data-driven structures[2] to suit the application needs. The access pattern being discussed here, deals at different level including general strategies in collection, representation, handling and access to spatial data. This section very briefly summaries the evolution in SDAP from a general viewpoint which is not restricted only to representation structure of the data, but considers various other attributes observed during the life-cycle of GI. The attributes considered for the categorization of patters include: sources of information; spatial, semantic and temporal granularity of the content; navigation style; source update style; number of users in workspace; access privileges to workspace; and data update style. 2.1

Monolithic Access Pattern

The monolithic access patterns in GI Systems is depicted in Figure 1. Here the data is collected by the publisher and distributed on the secondary storage media. Most conventional Remote Sensing and GIS applications falls in to this category.

Fig. 1. The Conventional Monolithic Access Pattern

The figure shows monolithic single user, off line, data access pattern that provides fixed set of thematic information collected mainly from remote sensing satellites, or created as a result of ground survey. Some of the issues here are the propagation of updated information, limited set of observables with fixed spatial and temporal resolution, and the requirement of the expertise, software and hardware capabilities to manage the GI. 2.2

Web Services Based Access Pattern

Addressing the shortcomings of monolithic patterns, the standardization efforts[3] under the auspices of OGC1 made it possible to allow the users access to GI and various geo processing services over the Internet. The end-user generally utilizes spaghetti model[2] to access the information by overlapping the layers containing 1

The Open Geospatial Consortium, Inc. : http://www.opengeospatial.org

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point, line or polygon features. User can discover and communicate with multiple servers to retrieve the thematic layers from multiple sources and render it simultaneously in the client applications like uDig2 . With this pattern, client can not only have instantaneous access to updated information, but also crate content that can be accessible by other clients.

Fig. 2. Interactive Access to OGC Services

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Collaboration Based Access Pattern

This pattern allows multi-user, online, read-write access to shared workspace. The users can manage their spatial content and allow access to others in shared environment. It enables the users to act as sources of information in a manner that many of the users can contribute the content to prepare a theme. One such experiment [4] demonstrated a collaborative effort of health professionals to build nation wide content using popular web based GI services. [5] and [6] provide an exhaustive list of interesting mash-ups that can be designed using the various web based GI services to build interesting collaborative applications. 2.4

Location Based Access Pattern

This technology enables GI access in pervasive environment where user can retrieve GI according to the dynamically changing coordinates. The issue of constantly adjusting navigation control as the coordinates are changed is tackled by keeping track of user movements using GPS, and sending the constantly updating position as navigation reference for GI retrieval. Applications like route planning, tracking, travel guides, and other interesting applications in [7],[8] provide successful implementation of this pattern. 2.5

Syndication Based Access Pattern

Patterns discussed so far are based on GI access in interactive manner. It may not be possible for users to constantly poll the servers to check for update. Syndication have been widely used by content management systems, where user can subscribe to the feeds of interest and using a feed reader user can poll the source URL for updates. The same strategy was identified[9] as suitable solution for GI access. The GI Sources may publish RSS feed with Geographically 2

User-friendly Desktop Internet GIS: http://udig.refractions.net

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Encoded Objects, and when feeds are received by client, the feed reader client application is modified to extract the spatial reference and render it on a map. This pattern allow single user, single/multi source, read-only access to syndicated GI content. The space, time and semantic granularity of the content is fixed by the content provider. 2.6

Semantics Based Access Pattern

Having addressed the syntactic heterogeneity issues, the recent focus of standardization[3] and research[10] community is now being diverted towards semantics of GI. In this approach, the domain knowledge captured and represented as Ontology is integrated at various steps involved in the GI. The experiments have demonstrated the effectiveness of semantics in improving the searching[11], navigation[1] and visualization[12]and portal based access [13]. Need for integration of semantic rule languages in GI is identified [14], for extending the existing web based GI services for future geo-spatial semantic web applications. 2.7

Event Based Access Pattern

This data access pattern allow single user, single/multi source, online, event driven read-only access to information based on the subscription conditions managed by the provider. A typical example of this pattern is implemented in location based service in which a person is notified the presence of a friend in particular proximity[8]. Event driven access to sensor data is also discussed in[15]. Location and time based access of information explained in [16] applied event based systems to provide tourism information. Following the Slice and Dice concept from business intelligence applications, [17]discussed integration of eventing information in space-time cube with map based interface.

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Grid Based Access Pattern

The basic issue of providing scalable and reliable access to computing and data resources to perform geo-spatial data management operations have been addressed in this pattern. When multiple Virtual Organizations(VO) collaborate to manage GI content, they require more control over resources to ensure the availability in dynamically changing environment. Grid is claimed[18] to bring required features; specially in the case of Spatial Data Infrastructure (SDI). A common approach in introducing grid technology is to enable current standard based services[3] in grid environment. Catalog service in [19] and Web Map Services in[20] explains this approach. Beyond the efforts of hosting such services in Grid Environment, few attempts have been reported[21] to integrate GI processing models with grid features.

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Requirement Scenario

The GI requirements in the planning phase are quite deterministic. Applications that deal with dynamic nature of systems where uncertainty is quite high

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include: Command and Control, Battlefield Management and Disaster Management. With uncertainly in availability of information sources, processing and storage resources and the end users in a dynamically altering environment, the methods of collecting, handling and publishing information needs modification. The SDAPs in such applications poses critical requirements that must be addressed. The following section identifies some issues in identifying the requirements and SDAPs that enable the required information flow. 4.1

Information Requirements of EOC

Determination of information requirement of an EOC is primarily based on the planning procedures that are reflected in their respective Operation Management Plans. The emergency operations with response activities in case of a disaster management scenario includes rehabilitation camps and handling medical, hygiene, food, sanitation, disposal etc that need reliable communication services. The information systems therefore provide theme based access to GI like medical camps, casualties, active respondents, critical services etc. In other words, depending upon the event and the planning of response activity, what information is to be collected and published in GI is identified. The critical issue here is that it is not pre-determined that who will be part of EOC, hence the detail planning steps can only be decided only after the event. This means that information requirements can only be determined only as the events unfold. Semantic Web Technology can play a critical role by selecting the rules to determine the information needs on the fly. 4.2

Relevant Spatial Data Access Patterns

Observations in recent disaster events has clearly indicated that respondents are mostly able to provide updates about the situation with the help of either personally owned or donated communication and computation devices. The argument is that careful integration of semantics in designing rule based eventing system for respondents and resource virtualization across EOC can provide basis to realize an EOC-scale GI management that will in-turn eliminate the trouble of information chaos. To support this argument two novel SDAPs are offered. (a) Rule Driven Event Based Access Pattern. This pattern is based on multi-user, read-write access to collaborative workspace and allows semantics driven eventing. It addresses the problem of collecting missing information that is required at specified granularity for the situation awareness. Information collection is triggered by rules specifying required additional themes at specific space, time and concept granularity. It must support both synchronous and asynchronous communication among collaborating users based on explicit requests or implicit interest derived from their concurrent role in the VO. (b) Role Driven Collaboration Based Access Pattern. This pattern is based on multi-user, read-write access to collaborative workspace and allows

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Role Driven Access to virtualized resources of EOC Grid. It addresses the issue of determining delegation of rights for the incumbent members for appropriate access to the grid resources. These authorized users can then utilize grid services to ensure reliable access to GI across EOC.

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Prospective Approaches Towards Solution

Figure 3 illustrates seven proposed key features in methods for handling data that will lead us towards achieving the identified SDAPs.

Fig. 3. Meeting EOC Information Requirements

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Considerations for Modeling the World

How many themes? The information requirements for disaster applications are somewhat different as compared to planning applications where snap-shot of natural and man-made features in the area of interest are primarily considered. For GI in disaster management scenario the set of desired observables also contains the respondent-actions, the instantaneous changes in resources etc. As discussed earlier, all the related concepts are represented and shared as Ontology. Thus the additional themes that will be required after disaster events can be inferred from the such Ontologies as indicated with arrow 2 in Figure 3.

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Fig. 4. Comparison of Two Approaches

What granularity? Granularity refers to the level of details at with the information is represented. Granularity of information is governed by the role, scope of activities and area of interest. The geometric resolution that defines the area of coverage, the temporal resolution that refers to the update of information and thematic access of most specific concepts that represents the area of interest most detailed level possible. Navigating to such required granularity is possible only if Ontologies are integrated with geographical representation. Thus adoption of semantics in representation of GI as indicated in Figure 4 can be followed as opposed to the conventional methods. What is the information need? Information need is the set of information that is required by an actor to take decisions and plan necessary action. It assumes availability of information at required granularity. Many valuable pieces of information may come only when asked for. Such information can only be collected if the need is identified and then the sources of information are polled at required time interval. The time interval and sources of information can only be decided by the policy. Hence there must be some mechanism that will allow conversion of such policy in to formal rules[see arrow 2 in Figure 3], that can be executed on detection of the event to determine the information need. What words to choose? The observations of the first respondents or victims that report the occurrence of the event for the first time are critical source of information. These verbal reports are to be converted to formal assertions to the systems with respect to some ontological representation[see arrow 3 in Figure 3]. The reasoner will in turn calculate membership of the asserted instances to

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possible classes represented in the ontology. This process is to be carried out by a non-expert receiving the calls at EOC. Hence, it is very essential for the system to allow search for proper concepts that will be used in representation. Ontological mapping[see arrow 1 in Figure 3] that integrates the concepts used by the user will help solve the problem. Which ontologies? With identification of the fact that to be able to provide discovery and navigation to meaningful information, not only words that are used by the users and domain experts needs to be mapped, but also it becomes essential to co-relate the concepts used in applications that will handle the information to maintain the proper information flow. Thus the application specific concepts must also be part of the ontology mapping efforts[see arrow 4 in Figure 3]. For example, if the disaster response policy suggest that if a request is not addressed by a legally responsible person for specific period of time, then volunteer must be identified and notification should be sent. To realize this requirement, the eventing system must go beyond the definition of a Subscriber and identify the hierarchy of the concepts that will match the policies of the EOC. We advocate the requirement to consider the application rules in representation[see arrow 5 in Figure 3]. Having identified the requirement of integration of ontologies that defines the Domain, Organization, and application concept needs to be mapped. A few formal approaches for instance EU-ORCHESTRA 3 are investigating on integration of Ontologies for smiliar objectives. 5.2

Considerations for Managing Grid Resources

Managing the Processed Information. The snapshots providing the situation awareness or predictive analysis created by the experts can be used to allow event driven access to end users. Hence collection of such processed information, must be managed effectively. The Grid Middleware for data management [OGSA-DAI4 ] provides services facilitating management of multiple data structure and representation, the lineage of data, modes of working, and other requirements during the life-cycle of scientific data. The utility of such services is envisaged in managing data sources and resources in EOC Grid that will enable role based access to collaborative workspace[see arrow 6 in Figure 3]. According to user’s role in EOC, the Grid security infrastructure can effectively utilize to assign the users specific roles in the VO to carry out operations for data management, computing resources management, task scheduling and other services offered by current Grid Computing environments. Managing User Communication. It is argued that in order to achieve the desired access patterns, the behavior of the GI system must be reactive and in case of disaster management application the goal should be to achieve pro-active 3 4

Orchestra Consortium: http://www.eu-orchestra.org/ http://www.ogsadai.org.uk/about/ogsa-dai/

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behavior. The concept of reactivity and proactivity can be archived first by appropriate representation of rules followed by integration of rules in appropriate communication among users. Up on arrival of a new fact, a series of rules can be triggered to enable collection, handling and notification of information. This requires tight integration of rules with synchronous or asynchronous communication with users exhibiting specific roles. Hence, is the requirement of integration of rule-driven approach in user communication to be archived to realize desired pattern[see arrow 7 in Figure 3].

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Sample Use Case

This paper identified requirements for the development of GI System to support proposed SDAPs in Semantic Grid environment. This section very briefly introduces a sample use case, details on the realization of which are beyond the scope of this paper. We discuss a scenario in which proposed SDAPs will be used by the respondents of a series of fire alarms after a disastrous event. Upon receipt of an emergency call, appropriate fire fighting and rescue team should be assigned for the response. This decision requires city or town level information. The information requirement of a fire fighter entering the building includes the information at building level with highest level of granularity in the details of the structure. A rescuer requires details about the occupants in the building. The emergency medical team will require frequently updated information about the availability of beds in the hospitals where the rescued victims are routed. Hence, the logical pool of respondents belonging to various departments, having a specific role to play in given situation is to be incorporated in GI, which will be taken as base for taking instantaneous decisions. The decision to poll the respondents that report detail information about the situation justifies the SDAP that govern rule based information collection. The collection and management of information received from respondents to create snap-shots of situation taken at specific time intervals, management and sharing among users justifies the SDAP that governs the role based access such data resources in ensuring reliable access to multi-granularity information to users and to the public at large.

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Discussion

This paper provided a brief account of evolution in Spatial Data Access Patterns to its current state. The emergence of semantic Grid technology have brought change the way the spatial data is accessed. It is noted that trivial use of semantics to extend meta-data capabilities and methods of managing data in grid environment will not suffice in harnessing the full potential of these technologies. To support this argument, various issues that must be resolved to meet the information need of Emergency Operations Center are discussed. Two novel SDAPs are identified that can help realize the goal to meet the information needs of multiple users in EOC. Subsequently the paper proposed the changes in using Semantics and Grid technology in GI Science to meet the challenging needs.

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