Java web server - The CaveatEmptor application access code that has consequences
The CaveatEmptor application access code that has consequences for the user interface has to be made, we ll naturally consider both. In order to understand the design issues involved in ORM, let s pretend the CaveatEmptor application doesn t yet exist, and that you re building it from scratch. Our first task would be analysis. 3.1.1 Analyzing the business domain A software development effort begins with analysis of the problem domain (assuming that no legacy code or legacy database already exists). At this stage, you, with the help of problem domain experts, identify the main entities that are relevant to the software system. Entities are usually notions understood by users of the system: payment, customer, order, item, bid, and so forth. Some entities may be abstractions of less concrete things the user thinks about, such as a pricing algorithm, but even these would usually be understandable to the user. All these entities are found in the conceptual view of the business, which we sometimes call a business model. Developers and architects of object-oriented software analyze the business model and create an object-oriented model, still at the conceptual level (no Java code). This model may be as simple as a mental image existing only in the mind of the developer, or it may be as elaborate as a UML class diagram created by a computer-aided software engineering (CASE) tool like ArgoUML or TogetherJ. A simple model expressed in UML is shown in figure 3.1. This model contains entities that you re bound to find in any typical auction system: category, item, and user. The entities and their relationships (and perhaps their attributes) are all represented by this model of the problem domain. We call this kind of object-oriented model of entities from the problem domain, encompassing only those entities that are of interest to the user, a domain model. It s an abstract view of the real world. The motivating goal behind the analysis and design of a domain model is to capture the essence of the business information for the application s purpose. Developers and architects may, instead of an object-oriented model, also start the application design with a data model (possibly expressed with an Entity-Relationship diagram). We usually say that, with regard to persistence, there is little Figure 3.1 A class diagram of a typical online auction model
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