An Introduction to National Geological Application Grid（NGG）
Yongbo Zhang1 and Shilong Ma2
1 (China Geological Survey Bureau, Beijing 10035, China)
2 (National Lab of Software Development Environment,
Beihang University, Beijing 100083, China)
Abstract
National Geological Application Grid, briefly NGG, is developed for applications of Chinese
national geological survey, for implementing resources interconnections, sharing and coordination.
The development and deployment of NGG have completed, a grid platform and an application
integration mechanism have constructed, and a prototyping system running efficiently has
implemented. NGG is now running on the three-layer network infrastructure in China Geological
Survey. So far NGG prepares itself well for the real productive applications.
Key Words: National Geological Application Grid (NGG), Grid computing, Service,
Groundwater resource assessment
1. Introduction
National Geological Application Grid, briefly NGG, is funded by High
Performance Computer and Software Program under National 863 Hi-Tech Program.
The project is carried out by China Geologic Survey Bureau collaborating mainly
with Beihang University. Grid is a new generation distributed computing technology
for integrating geographically distributed resources into a “super virtual computer” to
achieve complete share of computing resources, storage resources, data resources and
software resources[1, 2, 3]. As an application grid, NGG is developed for applications
of Chinese national geological survey, for implementing resources interconnections,
sharing and coordination. The development and deployment of NGG have completed,
a grid platform and an application integration mechanism have constructed, and a
prototyping system running efficiently has implemented. Now NGG has already
prepared itself well for the real productive applications.
NGG is running on the three-layer network infrastructure in China Geological
Survey Bureau. To meet the requirements in geological survey applications, China
Geological Survey Bureau, as the portal of the application grid and service
management platform for NGG, monitors and coordinates system running. As regional
centers for data-sharing, the regional Geological Survey centers deploy databases and
GIS software. The provincial Geological Surveys collect original data, provide
original data service, while the professional research centers with high performance
computing environments, process large scale data and share application software.
Supported by MAPGIS environment, NGG provides data and application
software sharing, including the following, 1. data sharing service for browsing and
querying data with MAPGIS, 2. ground water resource assessment service for
providing information about groundwater resource assessment, 3. groundwater level
forecast service for forecasting future groundwater level in specific areas with
dynamically observed data, 4. retrieval and synthesis of mine-shaping information
services in gird environment, 5. sharing of computing softwares for solid mineral
resource assessment.
2. The Architecture of NGG
NGG consists of basic services, a service flow constructor, tasks, a service flow
engine and a portal, where a basic service implements a basic function which can be
data service, transfer service, aggregation service and computing service in geological
applications; the service flow constructor integrates a task from basic services
according to service flow language specification of NGG; the service flow engine
parses, validates and executes services defined in a task; the portal provides interface
to users. For more details, see [11]. The architecture of NGG is shown as in Fig.1.
Fig.1：The architecture of NGG
In the above architecture, there are four important parts as follows.
Portal: Friendly interface to users, located in China Geological Survey Bureau.
Basic Services: services to implement atomic functions which can be data service,
transfer service, aggregation service or computing service in geological applications.
Core Services: MAPGIS Service (Note; NGG portal communicates MAPGIS
environment with MAPGIS services which provide the creation, browse and transfer
of geological vector data), Service Registry and Discovery Service (Note: NGG
communicates with China National Grid (CNGrid) [7] by Service Registry and
Discovery Service. NGG will register a node in CNGrid first, and then register all
basic services and tasks that NGG provides in the NGG node).
Service Flow: service flow constructor for constructing a task on the basis of
basic services, according to service flow language specification of NGG, service flow
interpreter responsible for parsing, validating, and executing services defined in the
task. Thus the service flow engine could query relevant services, bind services
dynamically and accomplish the user’s request.
A geological application is a task, which is a flow of services; all of services are
distributed deployed and registered in the central node of NGG; the task can manage
and monitor every inner service in it. Thus, a task is a service flow to accomplish a
geological application.
3. Service Flow for Aggregation and Coordination of Services
3.1. Aggregation and Coordination of Services in NGG
Services are deployed by different providers in NGG. A single service provides an
atomic function in geological applications. In many cases, a single service can not
accomplish a geological application, and it is necessary to integrate services into a
task. For example, in water quality evaluation application, user needs to retrieve dates
from the area, select ingredients from database usually in another computer, submit
them to several computers, and get final result for the evaluation. These services are
distributed among different nodes. User needs to complete every service step by step
manually which consumes user’s time and cost unnecessarily. The need to aggregate
and coordinate services is on demand very much in NGG. So it is necessary to
implement an automatic mechanism for carrying out the whole process of an
application in NGG to integrate geological applications.
3.2. Why to develop a new service flow model for NGG
The integration of services is not only to aggregate services but also to define the
relationships between services such as data transfer, status control and so on. Though
both WSFL and XLANG [8, 9, 10] are well developed service flow definitions, they
can not provide substantial support for geological applications in NGG. Applications
in NGG need to be organized dynamically. The state of a service usually affects
execution of the following services or the whole service flow. One service may be
employed repeatedly but it has different state control condition. Thus, we develop our
own service flow model for NGG based on the requirements of geological
applications.
4. A Service Flow Model for NGG
4.1. A service flow language for NGG
The service flow language for NGG is in form of three-layer structure, i.e., service
layer, activity layer and flow layer [11, 12]. Service layer provides basic information,
including service name, ID, address, status definition and data interface. The
interaction between services is defined on higher layer- activity layer. Activity layer
consists of a number of services and provides an independent function, which is a
light-weight flow. Activity layer describes the relationship of services and its major
attributes include name, type of activity, service list, pre/post conditions, data
interface and other constraints. Every service defined in the service list has its own
behavior, including state control, message transfer, data flow and so on. The
interaction between activities is defined on higher layer – flow layer. On the top of
this model, flow layer consists of a set of activities. Flow can accomplish a geological
application and its behavior is determined by activities. The major attributes of flow
include name, ID, data interface, control table, data table and activity list.
4.2. A service flow engine for NGG
In NGG a service flow engine is developed for creating and executing
automatically service flows for users. In the engine, the interaction between activities
is managed by the task, so users do not need to carry out every step manually
themselves.
The service flow engine for NGG consists of the following components. User
Interface, that provides users with a friendly interface to create service flow.
Syntax/Semantic Check, that provides simple syntax and semantic check of service
flow language. Service Discovery, that queries relevant services according to service
ID in service flow. Service Validate, that validates the status of the service found in
NGG. Service Binding, that binds logical service in service flow to valid physical
services. Execute, that executes service in service flow step by step. Service Monitor,
that monitors running status of each service in service flow. Service monitor will
catch any exception and submit it to Analyze/Plan module. Analyze/Plan, that
analyzes current circumstance. In the event of exception, rebind the running service to
other valid services and execute the service flow again.
5. Uniform access to heterogenous data in NGG
Geological data refers to all kinds of information in geological applications. Thus,
geological data may be in various forms, such as files, Oracle databases, SQL Server
databases and so on [4]. NGG presents the following solutions to provide uniform
access to heterogenous data. Define a uniform data access service by extracting a
model of heterogenous data access from different applications, and encapsulate it to a
standard web service [6] to provide services on higher level with uniform data access.
Describe input and output of data query using XML [5]. Then, convert XML input
into the corresponding data query languages during the course of application running
and also translate query results into XML. Compress the query results in XML form if
necessary.
6. An Example: A Task Running in NGG
Let us illustrate how NGG creates and carries out a task (service flow) by an
example of groundwater quality evaluation application in North China area. When
users submit the request of groundwater quality evaluation, NGG portal will accept
this request and communicate with MAPGIS environment to locate spatial data. NGG
portal forward these parameters to service flow engine, which creates an application
instance. The instance first queries relevant services from Service Registry and
Discovery and selects suitable services for binding, then startups profit service and
executes data service, transfer service and computing service step by step, finally the
instance finishes profit service, returns results to users and logouts. A simple process
is shown in Fig.2 and detailed process is shown in Fig.3.
fig. 2：Simple flow of groundwater quality evaluation
fig.3：Detailed flow of groundwater quality evaluation
6. Conclusions
NGG is a grid-based new generation geological application system that treats
resources as services and applications as tasks. NGG implements registry, discovery,
dynamical binding and invocation of geological services and achieves connectivity,
collaboration and sharing of geological resources. NGG provides services to
professional users who organize basic services into new tasks to solve geological
problems. To meet the requirements of complex geological applications, we
developed our own service flow model for NGG. As an example, in this paper we
illustrate how NGG Service Flow model creates and carries out a task (service flow)
by the application of groundwater quality evaluation in North China area. NGG is one
of the most important application grids in China National Grid (CNGrid).
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