At a minimum they are complimentary. This is the least technical question you will face. You must start with a Vision of what your data warehouse solution is to achieve and have a plan, at least at a high level, for rolling out iterative solutions. The rest of this paper will take you through the lifecycle of a data warehouse project, identifying where the critical technology choices need to be made and demonstrate how Oracle products can fill each technical need. If you are starting at square one, the first thing you must come to is an understanding of the business processes the data warehouse enables.
Some examples are managerial decision-making, product planning, market expansion, etc.
Spend some time with each functional group within your business and ask them what are their top 3 to 5 decisions. Typically this is enough to get them to start talking about their business intelligence needs. The people in your business generally have a very good idea of what they need to make decisions and many times can tell you exactly where the information lives in your organizations systems. You want them to talk about source systems and subject matter but try to resist the urge to get into the details that should come out in a detailed requirements session. Collect as much information as you can, even if it is not about data warehousing.