Thanks for the great responses from everybody and my apologies for the length of my response.
Having been a long term member of IPVM I was fully aware of the depth of knowledge of the IPVM community regarding access control and the wider security technology market which is why I posted the question although I get Eric's logic in wondering if the forum covered Access. I would not normally post anonymously but as this is specific to a client's security arrangements so I felt it was appropriate.
So getting back to my issue with integrating access control systems from different vendors and in an attempt to reply to some of the responses here is a bit of clarification.
The client is a large corporate multinational that operates facilities across the world. It has attempted to consolidate its access control systems across most of the security estate in the facilities it operates using Lenel. A majority of its facilities are now using Lenel giving a degree of standardisation across the company for access control.
However the company does inherit new facilities through acquisitions that use may not use Lenel. It also builds new facilities where the contract for the whole project is awarded to a main contractor and the provision for security systems is let for tender to local security contractor's as part of the total contract package. This produces a wide variety of solutions that often deviate from what is considered the company standard. There is no small resistance at a local level for the corporate security function to impose the company standard. To that end the company has implemented a PSIM solution ( I can hear John's exasperation from here) in an attempt to facilitate this deviation and incorporate orphan systems. This in itself is a whole other conversation I would like to have in the future.
Back to specifics:
In response to Brian's excellent point of hardware conversion through Mercury based controllers, this was an early consideration and may be possible (depending on model) but logistically it is difficult and might require a retrofit project which would need further funding and cause disruption. You are also correct in highlighting the fact that Lenel do not list any other ACS vendor in the OAAP document , and as John has highlighted all ACS vendors are reluctant assist with any integration that may see them lose the ability to lock out other vendors.
John, The integrator is a Honeywell VAR and is not a Lenel VAR which prevents him from offering Lenel as an alternative. In an attempt to avoid his design being binned he is clutching at straws and I have informed him as much.
He is talking about database interfaces, middleware, and data conduit options all of which scare the hell out of me and I have little confidence in his ability to make this integration work and I am sure there would be reliability and interoperability nightmares follow. For this reason I will be recommending that the system is Lenel and hope the client backs this decision.
Johnathon, It is interesting to hear from someone on the manufacturer side of the fence and you are correct both about the knowledge of both systems required and as I've already discussed above the VAR channel system often gets in the way of any possible integration. Access Control manufacturers are notorious (IMHO) for locking customers in and although some may now be making the right noises I have yet to see any of the majors implement anything meaningful.
All of this raises wider questions about system integration and interoperability of all electronic security systems. I have been an advocate for open architecture, open platform systems for many years based on IT standards and principals. Alas I feel our industry is no nearer to this than it was 5-10 years ago and as IPVM highlighted recently the acquisition of VMS and other software platform houses by big manufacturers is having an adverse effect in both choice and independence.
It is difficult as a Physical Security specialist to design systems knowing that you are potentially handcuffing a client to manufacturers and vendors with huge capital investment which they may regret soon after. BTW having used PSIM on a number of occasions it is not the answer.