TI is used for titles like "president" and "chairman", which can be used in certain circumstances without a determiner: after the preposition "as" or after verbs liked "name" or "elect".
+--------------CO-------------+
+--TI--+-Mp---+ |
| | | |
As president of the company, it is my decision
+----TI--+
| |
She was named president of the company
There are special dictionary entries for the no-determiner
usage of these nouns:
president.i chairman.i: {@M+} & (BI- or (Xd- & Xc+ & MX-) or TI-);
As this expression shows, such nouns can also be complements
of "be" ("She is president of the company"), using
BI-; and
they can also form comma expressions modifying a noun
("Jane Smith, president of the company, ..."), using
MX-.