OTTAWA -- The provocative opening statements of the Crown and defence might start Sen. Mike Duffy's fraud and bribery trial off with a bang, but what follows in the early stages is expected to be decidedly less dramatic.

The first few weeks are expected to dwell on the arcane world of Senate financial rules and regulations.

While the details of what constitutes a legitimate travel or per diem claim may seem downright dull, the answers will go the heart of the dispute over whether Duffy's expenses constituted fraud or not.

Duffy faces 31 charges relating to alleged breach of trust, fraud and bribery. In laying the charges, the RCMP described two "avenues" directly relating to the expenses issue -- his filing of living expenses for his secondary residence in Ottawa, and the filing of travel expenses for trips they allege were not for Senate business.

The expense issue continues to be a source of tension in the upper chamber, where the auditor general is scrutinizing the claims of dozens of senators -- some of whom say the way the Senate governs finances is confusing and arbitrary.

Some of the key questions at play at the trial include what constitutes a primary and secondary residence, and what is legitimate Senate business.

Before 2012, for example, senators weren't obliged to provide any proof of the Senate business they were engaged in on the road. What sorts of partisan activities are acceptable and which are not are also a source of debate.

Duffy has maintained that he broke no rules in submitting claims for a secondary residence in Ottawa, and that other expenses as improper were either legitimate or filed in error.

The trial, which will be decided by a judge rather than a jury, will begin with the customary opening statements by the Crown and by the defence. Those statements will span the four distinct sets of charges against Duffy, and will give the public a taste of how the case will unfold through to June.

The first witnesses, drawn from the Senate's back offices, will be examined and cross-examined on the particulars of the upper chamber's system of expenses and the rules that govern it.

The Crown will be represented by attorney's Jason Neubauer and Mark Holmes, and Duffy defended by lawyer Donald Bayne.

Neubauer and Bayne both told The Canadian Press they could not comment on the particulars of the case.

Bayne would only say that the "case is going to proceed and start on schedule." When asked if there was any contemplation of a plea deal, Bayne said "absolutely not."