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Kennedy, B. K. & Mayhew, B. D. 1999, in ASP Conf. Ser., Vol. 172, Astronomical Data Analysis Software and Systems VIII, eds. D. M. Mehringer, R. L. Plante, & D. A. Roberts (San Francisco: ASP), 383
StarView II: A Customizable Query Generation Tool
Bridget Kennedy, Bruce Mayhew
Space Telescope Science Institute
Abstract:
StarView is the user interface to the Hubble Space Telescope (HST) Data
Archive. It supports queries to the HST catalog, submission of retrieval
requests, data preview, and other archive-related functions. This
presentation looks at the StarView II effort to make a flexible, adaptive
framework for browsing astronomical catalogs. We discuss user interaction with the
customizable form, describe the use of Java Foundation Classes in implementing
the Model View Controller design pattern, and present design features that allow
simple, robust communication with third-party components added at run-time.
StarView II addresses two important concerns within the astronomical community:
the desire for a flexible catalog browsing tool and the need for an adaptive framework
capable of seamless interaction with current and future functional components.
Along with standard query forms, StarView II supplies an interactive custom query form building tool - the Customizer.
As shown in Fig. 1, the Customizer contains a keyword search panel and hierarchical displays of the data structure. With these catalog data browsing components,
Figure 1:
StarView II Customizer.
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the user builds custom query forms through simple point-and-click interaction. All
forms maintain their own state information, permitting asynchronous execution of
multiple searches. Each query form, along with its specific formatting
and state information, can be saved and retrieved using Java object
serialization.
StarView II forms implement the Model View Controller (MVC) design pattern through
encapsulated data modeling and selectable data views that interact via a controller. Clear division of functionality, and strategic use of interface classes,
result in a system that readily accommodates varying data sources and view components.
A simple two-dimensional vector was chosen for the structure of the
base data model. Application-specific knowledge of the data structure is contained
in a separate loader class that translates the underlying data into the generic two-dimensional vector. This allows the flexibility to replace or subclass the
loader class to handle
different data sources such as a flat file or internal memory structure. The rest of the
StarView II MVC architecture remains unchanged.
The prototype StarView II view components, list, text field, and table, are
extensions of Java Foundation Classes (JFC a.k.a. Swing). The MVC architecture built
into JFC provides an ideal backdrop for implementing the StarView II design. Using
Java interface classes, view components register interest in data model changes.
Once registered with the data model, JFC event processing keeps view components up-to-date with data changes.
View components register as listeners with the base data model through a minimally
specified interface class. The data model has no additional knowledge of the
characteristics of the
listener. Another interface expands this strategy by allowing third-party components to
assume the role of a StarView II MVC view. The only imposition, i.e., shared code, on
third-party code is implementation of the StarView II MVC component
interface. The end goal for StarView II is to allow run-time addition of these components.
Control, or data modification, is effected by a Query Processor object in response to
Search and Navigation user interface (UI) components. The Query Processor
interacts with a Database object. Each query form can search using a hard coded query, or, as in the
case of HST searches, generate the query at run-time. Automated query generation is
a complicated system and is isolated to run on a server allowing the option of turning off or bypassing this mechanism on a per form basis.
Data navigation refers to the ability to step and scan through the database using UI
controls. In considering navigation, it is important to discuss the StarView II ability to
keep various views in synch via registration with a common data model.
For example, as a user steps through records in a list box, the data model sends events
to all view component listeners. The view
components update their displays reflecting data associated with the record number
received in the event.
Historically, StarView has been used to browse the HST Data Archive. In setting goals
for StarView II, we recognized the need for a more flexible, robust browsing
tool and the fact that each user has a different set of functional requirements. We
accommodate unique functional requirements by providing a plug-and-play framework in
which a user can create a version of StarView tailored to specific needs.
The concept of Java interface classes provides the basis for communication between
StarView II and third-party components.
- Data pull interfaces allow a component to query StarView II for
available attributes and data contained within a form. Using this
interface, components can be instantiated at run-time and retrieve any
portion of the information contained on a screen.
- Data push interfaces allow a component to push generated data
back to a StarView II qualification form.
- MVC interfaces allow a component to register for data model
changes. The component receives event notification of a change and
then uses the data pull interface to obtain a specific attribute
location from the data stream.
- The Observer/Observable interface makes use of a user-defined
object class for data transfer between applications. StarView II is
required to have prior knowledge of the object's structure. This
accommodates more complex command interactions (Dolensky, Mayhew, &
Kennedy 1999).
StarView II's adaptive framework was well illustrated while testing the ease of
installation of JIPA (Dolensky et al. 1999) and SkyMap.
SkyMap is a component developed independently at STScI that plots HST
observations on an AITOFF projection.
The association established between SkyMap and StarView II
demonstrates a highly interactive relationship achieved through Java interfaces.
Our tests exercise bi-directional interfaces that send data to an external MVC
view and receive data from a third-party functional
component.
Figure 2:
StarView II/SkyMap Interaction.
 |
As an MVC component, SkyMap registers as a listener to the main data model and
receives data change notifications.
SkyMap responds to the event from the data model by highlighting the location
for the current record on the AITOFF projection.
As a member of a group of MVC components associated with a particular data model,
SkyMap interacts with other view components. When the mouse enters an
observation on the SkyMap, it sends a 'set current record' to the main data model. Other
view components receive an event from the model and update accordingly, achieving a
seamless interactive graphical display.
Finally, the SkyMap and JIPA tests both exercise the ability to push values into StarView II
from an external source. As the user points and clicks on the SkyMap display,
or the JIPA preview image,
the associated coordinates are pushed into Ra and Dec fields
on a qualification screen. These pushed coordinate values can then be used
for subsequent
searches.
References
Dolensky, M., Mayhew, B., & Kennedy, B. 1999, this volume, 454
© Copyright 1999 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
Next: Application of the Minimum Determination Algorithm to the Study of the Fine Structure in the Mass-Luminosity Relation and of the Nature of ``Overmassive'' Stars
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