All data gathered in or used by MAP are stored and made available
by the MAP Data Centre (MDC). This Centre is located at MeteoSwiss,
Zürich and is accessible through
the World Wide Web (Internet). The Internet has emerged from the
academic and research world to become a de facto component of
the Information Highway.
In the Web technology, a basic client/ server architecture supports all activities. Information is stored on Web Servers. Web clients, such as Netscape software running on a PC, Mac, or Unix workstation, request information by specifying the "name” of the information in a request transmitted across the network to a server. The server simply transfers the requested information back to the client - much in the same way as the various network file systems and servers operate on many networks today. The client formats the information and displays it on the user's screen.
Information is typically organized into "pages” each of which is up to several screen of material. Long pages can contain "hyperlinks” that allow a user to readily "jump” to another page which may actually be stored on an other server many kilometers away.
The information in pages is typically stored as text files, containing the information encoded in HTML - HyperText Markup Language. With HTML, pages can be readily created with formatted textual information freely mixed with multimedia content including graphics, audio, and even video, as well as the "links” that enable a user to "browse" from page to page across the Internet.
In addition to pages that are stored in files on web servers, the web technology provides a mechanism for dynamic information to be included in pages. The Web server in such cases uses a standard interface, called the Common Gateway Interface (CGI), to execute a separate program which obtains the dynamic information and returns it formatted as HTML.
Using this interface, it is becoming common practise for pages to include information from many kinds of sources. The external program might trigger a camera to capture an image and pass it back to the Web Server for delivery to the Client. On the Web there are pages which deliver images of highway interchanges, building lobbies, or simply interesting views from somewhere else in the world.
With the CGI interface, it is becoming common to extract information
from databases. The program executed through the interface is
simply a client of the database, and performs a query or stored
procedure operation to obtain the appropriate information and
form at it as HTML for return to the user.
The core activities of the MDC are illustrated in Figure 1. Oracle7™ is being used to supply information to a Web server for delivery to some client across the Internet.
The address where you can reach the MAP Data Centre (MDC) is
All you need is a Internet connection and a WWW-Browser. To use all the features of the MAP WWW-Server (Oracle WebServer 1.0) you will need a form capable browser like Netscape or Mosaic.
The MAP Data Centre home page is made up of two main components:
A public area for documents and an area for MAP members only with
specific MAP data. In the public part there are the MAP Design
Proposal, the Data Centre description, a Navigation Help (under
construction) and the MAP Newsletters.
High-priority data in the MAP member area are
The purpose of the MAP Data Centre (MDC) is to provide technical access to meteorological data for scientists working on topics related to MAP. On a policy level, a set of rules and procedures is required regulating the access to the data. This policy is defined in the MAP Data Access Policy, which serves as a basis for the access to the MDC.
In order to get access to data in the "supplemental" category, the user has to agree on certain conditions which are imposed by the data originator and which have been accepted by the IGP as appropriate.
The user wishing to get access to the "supplemental" data category
On receipt of the signed form, an account will be opened for the applying user and access to supplemental data will be granted.
To get to the MAP member area, you will need an account with username
and password. The Oracle Web Listener (Figure 1)
provides a Security Framework supporting two common authentication
mechanisms: Basic and Digest Authentication. Both mechanisms allow
certain directories to be protected by username/password combinations.
However, Digest Authentication transmits encrypted passwords,
while Basic Authentication does not, and is included to support
third-party web browsers not capable of Digest Authentication.
The Oracle Web Listener is designed with security extensions in
mind, allowing any HTTP based security scheme to be added in future
releases. The next release of the Oracle WebServer will support
the security mechanism(s) standardized by the W3C (World Wide
Web Consortium) for encrypted data transfers. Currently, both
SHTTP (Secure HTTP) and SSL (Secure Sockets Layer) are proposed
standards (Oracle, 1996). In addition enforcement of security
in the access of the MDC, all activities are logged.
In general there are two kinds of data available at the MDC: table-orientated
data like station-, radiosonde-, aircraftdata, etc. and file-orientated
data like satellite- and radar images. From the point of the user
it does not matter which kind of data he wants to access. For
example if you want a Radar image from the Brig case, you must
go first to the MAP member main page. In Figure 2
you can see the hierarchy of the MDC documents. Now you follow
the hierarchy until you reach the page with the radar images name
and short description table. Now click on the name of the radar
image you want and you get back the radar image as a "gif-image".
If you want an email address from a MAP member for example, first
you go to the MAP personnel information page (see Figure 2).
Now you can choose the fields of the table you want. In the "where
field" you fill in the name you search for and then press
the query button. You will get a table back from the MDC with
the fields you had selected before, and the name or names that
are found in the MAP database. In a next step we will allow the
users to make more complex SQL queries.
There are two ways for any data provider to send data to the MDC.
The providers can reach the MDC by anonymous FTP or by establishing
a database connection directly to the MDC.
The anonymous FTP address of the MDC is ftp.sma.ch (129.132.77.123). To login use "anonymous" as username and your email address as password. Put the data in the directory "/outgoing/map" and send a email to the MDC that the data are ready.
| Accepted file formats are: | ||
| ASCII file | ASCII file with a short description at the beginning of the file or in an extra file. (To compress the ASCII files please use gzip or pkzip) |
| Excel file: | Microsoft Excel version 3 to 7 are accepted | |
| GIF format: | All images in the MAP database are stored in "GIF format" (it is a common and compressed format) |
If you have data in an other format, please contact the MDC before
you send the data to MDC.
For any data provider with an Oracle8 database it is possible
to establish a database link or a snapshot with the MDC. If a
database link or snapshot is not possible (Internet or security
problems) then you can access the MDC with SQL*Net by your own
SQL*Plus. It is important to remember that you can only send data
to the MDC, but you have neither access to the MAP member data
area nor to the MDC file system.
Internet's unbroken growth and recent fundamental topology changes
within the international backbone occasionally cause some nasty
connectivity problems. In most cases, the problem could be identified
as hosts sending out IP packets with too small initial TTL (Time
To Live) values. Worst case maximum hop counts of up to 40 can
be observed nowadays. TCP and UDP initial TTL values should be
set to a "safe" value of at least 60 today. Look at
Internet Help page (Figure 2) for more background
information.
References
Oracle, 1996: Oracle WebServer. Oracle Corporation World Headquarters, 500 Oracle Parkway, Redwood Shores, CA 94065 USA, Part #: A34211.
MAP Data Centre - May '05 - MAP WebMaster
