So what exactly does an OMS do? I think I asked this questiion about a year or so ago, but now I have more experience under my belt and may be able to ask a more specific question.First, it seems pretty obvious to me that the purpose of an OMS depends on the organization:1. An OMS for a market maker will receive customer (and internal trader) buy/sell orders. This OMS has to keep track of accounts, their positions, their P&L, etc. It also has to maintain a market-maker wide 'book' which will also be used to show top quotes to the market. When an order comes in, if the stock is in firm's inventory, the system sends out an execution report to the customer and allocates some number of shares to the customer (and removes it from internal inventory). If the stock is not in internal inventory, the order is perhaps sent out to the market2. An OMS for a broker receives an order from a customer and either sends the whole thing to a market maker or applies some sort of strategies (break up the order into smaller orders, trade along with the nbbo, whatever). Once the broker has executed the whole order, the customer is sent back a complete fill.3. An OMS at a hedge fund may just be a interface to send orders (and receive fills, cancels, etc.) or also maintain list of the fund's positions, open orders, risk, smart router, market visualizer, etc.Are the above assumptions right? Can someone offer more specific (minimal or expected) requirements of OMSs for various organizations?I haven't found any books, websites or forums which answer this question. Apparently, people learn by working with those who already have experience. I have also recently started learning a bit about FIX. I tried earlier but I just didn't get it until recently I had to process some messages at work (very basic level). I'd like to learn about OMSs (which seem to be the heart of trading firms) without waiting to get an opportunity to work directly with them (which may not come for years).Thanks!

I can't speak to the other 2, but at least at the hedge fund I work at, #3 is pretty spot on. We use an OMS mainly to enter orders filled away from our PB. Orders filled electronically with the PB are auto imported into OMS and we just confirm that fill details match what we have. Sorry that I don't have more info, I don't have much experience on the other side of the trade.-Dylan

Some companies might not have the same ideas as others about what an OMS is and how to distribute it.Some companies might do it all in the GUI i.e. a very thick client. Some might have one server application do everything. While others will actually distribute the load between several servers.I am only going to comment on your assumptions because we could talk about this forever.1. The OMS should not care about or deal with P&L. Distributed trading systems typically have a component which deals with pre-deal risk. This component usually deals with current positions and potential positions (orders currently working) to ensure that a user does not exceed the limits assigned to him from the risk desk. Typically the OMS will communicate to this component to ensure that the order is valid. I am not sure what you mean by Quotemarket-maker wide 'book' which will also be used to show top quotes to the market. I will assume that you are talking about highlighting your current orders in the market against the BBO. The OMS shouldn't directly deal with this. I think you have some broker functionality in the mm section of you question.2. This depend on the broker. Some brokers only send email confirmation to their clients because a back-office feed doesn't exist. If they have a nice distributed system then they will use some type of parent / child pattern.Most OMS functionality will be defined on what the company is trying to do. There is a huge difference of functionality between companies etc... Do you have a specific questions because like I said we could discuss this all day with several different viewpoints. Another thing to keep in mind is the number of exchanges you system support and how many regions are using this software.

Some OMS acts as a end to end application, customized according to the brokers system. apart from front office order management, risk management it may encompass the Analytical reports, Commission and refund calculations of brokers and other features.