Explanation of inviting, to be held and being held

[guest121]

could u please clarify the meaning of the following:

1. we thank u for your letter dated inviting us to attend the workshop to be held in London on 5th August 2006.

1. we thank u for your letter dated inviting us to attend the workshop being held in London on 5th August 2006.

please tell me the meaning and structure of inviting... also to be held in (1) and ... being held in (2).

Thanks once again

[Mister Micawber]

.
u = you.

...dated 15 August inviting... = ...dated 15 August [that is] inviting... -- inviting introduces a nonfinite clause acting as an adjective that modifies letter. (Dated also introduces a similar clause with a similar purpose.)

To be held and being held also introduce nonfinite clauses acting as adjectives modifying workshop.
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Native English teacher at Mister Micawber's