As Natan Gur writes, Architecture is defined as "science of designing and building buildings; layout, formation, arrangement; building style or method; design of a structure and its components (Computers)". Architecture therefore is the method of finding out what are necessary and sufficient components and their relation in order to create a new structure (Building, Computer or software). Architecture is a holistic view of the structure.
The architect is the main technical contact for a BPX. Their collaboration is crucial for the success of a project.
Especially important in today's business world is the understanding of the Enterprise Service Oriented Architecture (Enterprise SOA). The design and the use of services is the fundament for the business process. For a BPX the Enterprise SOA is an intermediary step for what we really want: a business process architecture, with mapping the process steps to the services. This is a top down approach. You may also compose a process from services at hand (ad hoc design, SAP portal).
In computer science the term architecture is deprecated. Use the term design instead.