Therefore, the domain knowledge along with the file name convention of each data provider is necessary for the implementation of agent classes. For example, the URL of an IGS ephemerides file is 3.sp3.Z, from which one can infer that it is a rapid file and the GPS date is the fourth day of the week 1324. URL, create time, etc.) and contents of data files are useful to discover RSS-related information. Different data providers use different methods to describe their data, most of these descriptions are given as textual notes, which human must interpret. The effort required to create RSS feeds for diverse data sources is not trivial. For example, the class creates a RSS feed for IGS ultra-rapid GPS satellite ephemerides and the clock parameter data, the class creates a RSS feed for IGS ultra-rapid tropospheric zenith path delay data, and the abstract class with its subclass defines the access interface for RSS Feed Publisher to create agent objects. Each subject class inherited from known as an agent must implement the getRSSFeed function. The class is an abstract class that defines a getRSSFeed function, the output of the getRSSFeed function is a XML document which represents the RSS feeds of the data source.
JAVA RSS FEED READER EXAMPLE SOFTWARE
Figure 3 illustrates the class diagram of this software component, in which the Abstract Factory Method design pattern (Gamma et al., 1995) is adopted. The External Data Proxy will create RSS feed items for these data sources. Usually these data are available for downloading through providers’ Web or FTP servers. For some post-processing applications, external GNSS data such as IGS ephemerides and meteorological data are required. It also can be saved in a native XML database (NXD), in which all elements are saved in native format. For instance, it can be saved in a relational database management system (RDBMS), in which each element is mapped to a database field. There are several options available for this database.
JAVA RSS FEED READER EXAMPLE GENERATOR
Once an RSS feed item is created, RSS Feed Generator saves it to a database. Though the element is defined as an optional element, it allows an RSS aggregator to make a distinction between multiple items. The element contains a string which is assigned by the system as a globally unique identifier for the item. The time when the item is published, is given in the element, and the format of the date/time information should follow Requests for Comments (RFC) 822 which is a Standard for the format of Advanced Research Projects Agency (ARPA) Internet text messages (Crocker, 1982). As an example, the station name, start time, end time and observation interval of the RINEX file are listed in a HTML table. HTML tags are also supported in this element. The element includes the description of the item. The element provides the URL of the element, which provides an access point for RINEX file downloading. An element contains a element, which gives a title of the item. In RSS 2.0, description of a GNSS data file is represented by an element and its sub- elements. An example of such a data structure is provided in Figure 2. In the proposed platform, RSS Feed Generator is a software component that creates RSS feed items for GNSS data files. The detailed functionality of these three components and the control/information flows between them are described in the following subsections. All these items are syndicated and published online as RSS XML documents. RSS Feed Publisher is an online web application, which replies a user’s requests and retrieves RSS feed items from the database and External Data Proxy. data sources and to generate RSS feed items in real time.
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