L-system generator
(→L-system string interpretation) |
(→L-system string interpretation) |
||
| Line 77: | Line 77: | ||
|- | |- | ||
| '''{''' | | '''{''' | ||
| − | | Start | + | | Start cyclic block. First topic in the sequential block is associated with the topic before the block. Last topic in the cycle block is associated with first topic in block. |
|- | |- | ||
| '''}''' | | '''}''' | ||
| − | | Close | + | | Close cyclic block. |
|- | |- | ||
| '''-''' | | '''-''' | ||
| Line 91: | Line 91: | ||
| Reset topic counter. | | Reset topic counter. | ||
|} | |} | ||
| − | |||
== Limitations == | == Limitations == | ||
Revision as of 12:12, 11 December 2008
Wandora's L-system generator is used to construct topic map graphs using formal grammar called L-systems. L-systems are generally known as iterative computational methods used to generate self-similar fractals, usually plants and other biological organisms.
Wandora's L-system generator starts with File > Generate > L-system generator.... Option opens a dialog with two tabs: L-system and Parser. By default the L-system tab is active. L-system tab is used to enter actual L-system to the generator. Below is a snapshot of L-system tab view in Wandora. Tab contains also drop-down-selector to select ready-made L-systems. User can also store his/her own L-system by clicking new button and entering name for the L-system into a dialog Wandora opens. Wandora stores L-systems to options.
L-system contains in Wandora
- An initiator
- One or more rules
Initiator is the first line in L-system. It is usually an alphabet or set of alphabets. Initiator initializes the L-system string. For example, the snapshot above has an L-system with initiator x.
L-system rules have always two parts: Predecessor and successor. Rule is executed whenever L-system generated string contains predecessor. Predecessor is replaced by successor string during the rule execution. For example, the snapshot L-system above contains one rule where predecessor is x and successor is a[xx].
L-system execution continues only limited time. Each execution step is called iteration. Text field below the L-system definition text area contains number of L-system iterations. As L-system string may grow exponentially large it is suggested you not to use more than 10 iterations unless you are sure about the outcome of L-system.
As iteration continues the initiator string is gradually changed by rules. For example examining the snapshot above initiator x is changed:
0: x 1: a[xx] 2: a[a[xx]a[xx]] 3: a[a[a[xx]a[xx]]a[a[xx]a[xx]]] 4: a[a[a[a[xx]a[xx]]a[a[xx]a[xx]]]a[a[a[xx]a[xx]]a[a[xx]a[xx]]]] etc.
As you notice, the string grows very rapidly.
L-systems itself carry no interpretation of generated string. Generated strings are semantic free, you could say. This reflects to Wandora's L-system generator feature also. L-system string generation is separated from the interpretation. Interpretation is handled by special L-system string parser that reads the generated string and interprets each token in the string.
L-system string interpretation
Typically L-system string is interpreted to turtle commands such as move forward, draw line, and turn left or right. However, such interpretation has implicit assumption of external environment. If you consider plain graphs, there is no such external world we could refer. Thus Wandora interprets L-system string little different compared to usual L-systems. The vocabulary and it's interpretation are explained in the table below.
General principle is that each alphabet in vocabulary creates a topic and associates it with some other topics, usually at least the previously created topic. When topic (excluding named topics) is created, global variable called topic counter is increased by one. When L-system string parsing starts, topic counter is 0. Topic counter is used to derive topic's identity. Thus, topic is merged with existing topic with same topic counter.
Different parenthesis are used to control branching of the graph. Branching means that at least first topic in the branch is associated to the "body". Branch typically ends (closes) somewhere in the string and graph generation returns to the "body".
Capital alphabets are used to create named topics. Named topic has strong identity. This means that named topic is always same. Named topics allow you to refer same topic everywhere in the L-system string.
Coloring of associations and topics refers association and topic typing. When we say topic is colored by e then topic is typed by topic derived from alphabet e. Same applies to associations. When association is colored by e then association type topic is derived from alphabet e.
| Alphabet(s) | Interpretation |
| a | Creates a topic and associates it with previously created topic. If no previous topic exists, no association is created. |
| [A-V] | Create named topic and associate it with previously created topic. Named topic merges with previously created topic with same name. Unfortunately vocabulary supports only 23 different named topics. |
| [eiouy] | Create a colored topic and associate it with previously created topic using colored association. Colored topic means here that topic is typed. Colored association means here that the association type is different. Notice the set is equal to vowel characters (a taken out). |
| :[a-zA-Z1-9] | Change global color i.e. topics and associations are colored after this point. |
| :0 | Reset global color. |
| ( | Start sequential block. First topic in the sequential block is associated with the topic before the block. Topic's created after sequential block has been closed are associated to topics created before the block. Blocks are used to branch graph. |
| ) | Close sequential block. |
| [ | Start parallel block. All topics in the parallel block are associated with the topic before the block. |
| ] | Close parallel block. |
| { | Start cyclic block. First topic in the sequential block is associated with the topic before the block. Last topic in the cycle block is associated with first topic in block. |
| } | Close cyclic block. |
| - | Subtract topic counter by one. The effect is that next topic is merged with previous topic. |
| + | Add topic counter by one. The effect is that there is a gap in topic numbering. |
| 0 | Reset topic counter. |
Limitations
- The L-system interpretation allows only binary associations. You can't generate associations with three players for example.
- The L-system interpretation supports only 23 [A-V] different "static" topics.
