GML Differs from KML (Keyhole Markup Language), well known for its association with Google Maps. XML grammar is used to describe vector, raster and sensor data. Geographic Markup Language (GML) conveys spatial data content. There are a variety of XML grammars defined for specific purposes. This ensures that "Stephan Lane" is a street name and not a person's name, for example. XML provides a general way to attach meaning to data. Web services send and receive eXtensible Markup Language (XML). These are also protocols for exchanging map data, much like HTTP and FTP. Provides data access with full vector intelligence (slower).Provides full vector representation (GML) of the spatial data requested.Displays data as a raster only (faster).Creates a raster image of the spatial data requested.The most common Web Services are Web Mapping Service (WMS) and Web Feature Service (WFS). Doug Nebert of the Federal Geographic Data Committee (FGDC) Secretariat provides an introduction to geospatial web services and how they work. Watch the video, Geospatial Web Servers (11:48). There are web services specifically tailored for spatial data. Web services provide remote access to data and processes using defined protocols. Interoperability for spatial data revolves around web services built on Internet protocols. Internet protocols (TCP/IP, HTTP) provide interoperability for computers. There is a defined process, starting with OGC members and ending with public comment. The Spatial Data Interoperability Standards are published by Open Geospatial Consortium ( OGC), a voluntary organization with its primary support from vendors. ICANN coordinates IP addresses worldwide, amongst other Internet-related tasks. Steve Crocker is now chairman of the board of ICANN, the Internet Corporation for Assigned Names and Numbers. RFCs were created by Steve Crocker, and were edited by Jon Postel until Postel died in 1998. RFCs guide programmers in what to expect from each other's works. Protocols become real when people write software that uses them. Famous RFCs (originals, now superseded) include the following: Protocols are open, starting with a published RFC (Request for Comments). Internet protocols are published by the Internet Engineering Task Force (IETF). A URL beginning with FTP: is used to transfer files from the server to a client. For example, FTP is the protocol used to access a site that stores files. The browser can also interpret protocols other than HTTP. At the beginning of the web address, the protocol, is used to tell the server the protocol to expect.įigure 2 – Browsing to the Open Source GIS website HTTP specifies how web browsers and web servers communicate. Other common protocols include SMTP (simple mail transfer protocol) sends email, SSH (secure shell) provides for a secure interactive terminal session, and IMAP (Internet message access protocol) reads email. HTTP (hypertext transfer protocol) is used to transfer web pages. For example, FTP (file transfer protocol) is used to transfer files. Other protocols layered on top of TCP/IP define what those bits mean. TCP/IP gets bits from machine to machine in a reliable way. A protocol is a standard way or set of rules to get information from one machine to another. The Internet uses protocols for communication. Legend has it that Vint and Bob drew the basics of TCP/IP on a napkin in a bar in Palo Alto. Vint Cerf is sometimes referred to as the "father of the Internet". TCP/IP was invented by Vinton Cerf and Robert Kahn. TCP/IP (Transmission Control Protocol/Internet Protocol) is an internetworking communications protocol. TCP/IP, represented by the cloud in Figure 1, handles the details.
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