For a particular Videotex service a page definition is produced for each Videotex page. The page definition defines
The page definition is a list defined within a text file -- typically, one file would contain all the page definitions for a given Videotex service.
An example page definition is as follows:
(page "LOGON"
(neighbours "START"
"NewsFlash"
"INDEX"
"SpecialOffers"
)
(matchFields
(0 24 "0001")
)
(canMap
(20 17 "ABTA")
)
(inputFields
(user 20 29 5)
(password 21 12 5)
(reference 21 22 3)
(prompts 21 38 1)
)
(extractFields
(user 20 29 5)
(password 21 12 5)
(reference 21 22 3)
(prompts 21 38 1)
)
#
## triggers
#
(before
(if (mapper.isCursorOnAt 20 29)
(mapper.newPageEvent.set)
)
)
(hotPatch 20 29
(mapper.detectNewPage 20 29 "hotPatch")
)
(messageRow 23
(Airtours_handleError mapper)
)
)
page
The order of page elements is not important.
Many of the page elements can contain Carapace script expressions to evaluate. For such expressions, the evaluation environment is fixed and the following script variables are defined:
| name | type | description |
|---|---|---|
expr |
Object |
the expression to evaluate |
screen |
Screen |
the screen module which contains all the text on the Videotex page and can have data extracted from it |
env |
HashTable |
the mapping environment -- the contents of this persist for the lifetime of the mapping session |
page |
VideotexMapPage |
the definition of the current page being mpapp |
upload |
HashTable |
data loaded into the mapper for upload to the service |
mapper |
VideotexMapper |
the mapper object itself |
The following table shows the types of page elements
| element type | description |
|---|---|
| neighbours | defines the likely neighbouring pages for this page on the Videotex service -- this improves the search for identifying an incoming page |
| matchFields | defines fields on screen which, when they all match the supplied data, provide a way to identify this screen and discriminate it from any other on the service |
| match | a more general way of identifying a screen than the useful, but limited, matchFields |
| inputFields | defines the locations, sizes etc. of the input fields for supplying data to the Videotex host |
| extractFields | defines the locations, sizes etc. of areas on the page which hold data which should be extracted |
| options | defines the options available on this page available for selection by the user |
| translateOption | translates the option to the correct Videotex data |
| canMap | defines a test to determine if the page is sufficiently complete so that it can be mapped |
| map | defines the map to extract the data from the page and convert it into a more useful format |
| htmlTemplate | name of the HTML template which is used for mapping this page -- only of relevance if the map is from Videotex to HTML |
| before | a trigger which fires the first time the page is identified |
| after | a trigger which fires when a Videotex 'reset' character is received -- since this destroys the current page |
| home | a trigger which fires when the Videotex 'home' character is received which puts the cursor to position 0,0 but which does not clear the screen |
| cursorOn | a trigger which fires when the cursor is turned on |
| cursorOff | a trigger which fires when the cursor is turned off |
| messageRow | a trigger which fires when a message is received on the supplied row of the screen -- this only fires when the cursor leaves that row after having entered it |
| hotPatch | a trigger which fires when the cursor enters the given rectangular patch of the screen |
| exitZone | a trigger which fires when the cursor leaves the given rectangular patch of the screen |
| hotText | a trigger which fires when the given piece of text appears on screen at the supplied position |
| invariant | a trigger which fires when the given piece of text is no longer on screen at the supplied position |
Defines the likely neighbouring pages for this page on the Videotex service -- this improves the search for identifying an incoming page.
The search algorithm for identifying a page is as follows:
Many Tour Operator services have a region on screen which is used as the page identifier --
this is equivalent to the page number in a book. The matchFields element
defines regions on screen where certain pieces of text must exist for this page definition
to match. Multiple such regions can be defined -- in this case all such text
fragments must match for the page definition itself to match.
A more complicated example which will be satisfied only when both the words "Hello"
and "THERE" are matched at the given positions -- note: matching is case sensitive:
(matchFields
(0 10 "Hello")
(1 11 "THERE")
)
For those services which are more cunning about page identification, see the match page element.
The match page element contains the symbol match
followed by a single Carapace script expression to evaluate. If the expression
evaluates to () the empty List then the
page is not matched -- otherwise, the page matches.
For example, if we identify a page by the existence of the word "Special-Offers"
which may appear anywhere on screen, the following match element will work:
(match
(screen.find "Special-Offers" 0 0)
)
A list of fields on screen which are used for data input is defined in the
inputFields page element as follows:
(inputFields
fieldDefinition
....
fieldDefinition
)
The extractFields page element labels areas of the screen to extract -- these
can then be mapped further to turn the page data into a more useful format.
(extractFields
fieldDefinition
....
fieldDefinition
)
Many Videotex pages offer the user a list of options -- evaluate of the
second item in the options page element returns these options.
If this expression is a Symbol it is taken to be the
name of a function which has the following prototype:
(defun List functionName ( (screen Screen)
(page VideotexMapPage)
(env HashTable)
)
)
Some pages have a fixed list of options -- others require looking at the page data to determine if an option is available.
A simple options element is as follows:
(options (list "more" "previous" "index")
)
The second item in the translateOption page element is an expression which
takes the selected option
and converts it into the relevant data to send to the Videotex host.
If this expression is a Symbol it is taken to be the
name of a function which has the following prototype:
(defun List functionName ( (option String)
(screen Screen)
(page VideotexMapPage)
(env HashTable)
)
)
In all other cases, the item is evaluated. The evaluation result is allowed to be a String provided there is only one input field on the current page. Otherwise, the value must be an attribute-value list where the attributes match the names of input fields on the current Videotex page.
The canMap page element forms the test to see if the page
is sufficiently complete for mapping to take place -- the second item in the
page element is the test expression.
If the test expression starts with an Integer, then
it is required to identify a piece of text on screen e.g.
(canMap
(20 17 "ABTA")
)
ABTA appearing on screen at row 20, column 17.
In all other cases the test expression is evaluated -- if the result is the empty
List () then mapping cannot proceed, otherwise
the page is deemed complete.
One common such test is to check if the page cursor is on i.e.
(canMap
(screen.isCursorOn)
)
The map page element defines the mapping for the Videotex page -- e.g.
this could extract the page data and turn it into an XML object. The second
element in the page element is the map expression.
If the map expression is a Symbol it must be the name
of a function with the following prototype:
(defun Object functionName ( (screen Screen)
(page VideotexMapPage)
(env HashTable)
)
)
When used in conjunction with the XML Videotex Translator the returned object should be of type Xml.
The htmlTemplate page element names the
HTML template
to be used for mapping this page -- only of relevance
if the map is from Videotex to HTML.
E.g.
(htmlTemplate "logonPage.htm")
The before page element defines the trigger which fires the
first time the page is identified. The second element in the page element
is the trigger expression.
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
A common before trigger is to record the detection of a new page
e.g.
(before
(if (mapper.isCursorOnAt 20 29)
(mapper.newPageEvent.set)
)
)
The after page element defines the trigger which fires when the
'reset' Videotex character is received. This character moves the cursor to row 0, column 0
and clears the screen. The second element in the page element
is the trigger expression.
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
A common after trigger is to store the extracted data from the page
e.g.
(after
(env.set "history" (cons (mapper.mapCurrentPage) (env.get "history")))
)
The home page element defines the trigger which fires when the
'home' Videotex character is received. This character moves the cursor to row 0, column 0
without clearing the screen. The second element in the page element
is the trigger expression.
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
The cursorOn page element defines the trigger which fires when the
Videotex service turns the cursor on for the current page. The second element in the
page element is the trigger expression.
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
The cursorOff page element defines the trigger which fires when the
Videotex service turns the cursor off for the current page. The second element in the
page element is the trigger expression.
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
The messageRow page element defines the row where messages are received and
the trigger which fires when the Videotex service sends a message.
Typically, Videotex services reserve a row (e.g. row numger 23) for the display
of messages to the user.
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
A common messageRow trigger is one which ignores certain messages
and raises an error on any others e.g.
(messageRow 23
(handleXYZserviceError mapper screen)
)
The hotPatch page element defines a rectangular region on screen
where the trigger fires when the cursor enters that region. There are two
forms of the hotPatch page element e.g.
(hotPatch 10 20 (messageBox "HERE"))
(hotPatch 10 20 2 3 (messageBox "HERE AGAIN"))
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
The exitZone page element defines a rectangular region on screen
where the trigger fires when the cursor leaves that region. There are two
forms of the exitZone page element e.g.
(exitZone 10 20 (messageBox "LEAVING HERE"))
(exitZone 10 20 2 3 (messageBox "LEAVING HERE AGAIN"))
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
This is a particularly useful trigger for extracting and storing the data from a page.
The hotText page element defines a position on screen
and a text fragment such that the trigger fires when that piece of text
appears on screen at the given position e.g.
(hotText 10 20 "Error" (messageBox "GOT IT!!!"))
The result of the trigger expression evaluation is ignored -- the trigger is useful by its side effects.
The invariant page element defines a position on screen
and a text fragment such that the trigger fires when that piece of text
is no longer on screen at the given position e.g.
(invariant 10 20 "Error" (messageBox "LOST IT!!!"))
The result of the optional trigger expression evaluation is ignored -- the trigger is useful by its side effects.
| Contents | Current topic: videotex | Related topics: Carapace Hub |