Domain Layer

The next three layers reside on an application middleware server, although in some systems, there is a further physical separation between the presentation layer, which runs on a different hardware from the domain and data access layers. If EJB is used in a J2EE application, the presentation layer runs on a Web container and the domain layer runs on an EJB container. With the EJB local interface in J2EE 1.3, the separation becomes unnecessary, which eliminates the network overhead between the two. 

The business layer (or domain layer) is the center of the system that does the real work. It implements all business logic and workflows. In J2EE, EJB can be used to implement the Business layer. However, you can also use Plain Old Java Object (POJO) with an object-relational mapping tool or direct JDBC API to do the job. 

Web-based systems offer several advantages over rich client easy to deploy and access, easy to scale (by adding more hardware resources to the application server), and shared computing resources (CPUs, memory, database connections). However, most of the information this book presents is not limited to Web-based applications. It promotes the loosely coupled Presentation Layer and Domain Layer so that business logic can be reused no matter what GUI technology is being used. 

There are a few design options for the Data Persistence Layer. Here we use the Data Mapper Pattern (Fowler, 2003b). The reason is that we want to separate the domain layer and the database schema and allow them to evolve independently. 

Formal and refined document contents models are needed to supply all information which is later used for the definition of integration rules. Currently, only type hierarchies are used, defining all entities and relationships that are to be considered during integration. Future work will deal with adding more structural information. These models are similar to the document content models of the application layer which, at the moment, are not elaborated. However, they are much more detailed and have to be formal. Also, further information is needed here that is of no interest on the application domain layer. 

Not all informa tion of document contents models of the application domain layer is needed for the process of integrator development. Only the parts describing relations between documents need to be regarded. 

Link types usually have to be elaborated manually. They represent types of increments to be connected by an integrator. Today, the interdocument relationship models on the application domain layer are not of enough detail. 

On the application domain layer (a) of Fig. 6.1, there is only one model, however being composed of different submodels, see Sects. 2.6 and 6.1. The same is true on the platform layer (e). Correspondingly, the mapping layer is less critical. The UI layer is handled implicitly, as has been argued. Summing up, the main problem is on the conceptual realization layer (see Fig. 6.9). 

N.P. Zhuk and D.O. Batrakov, Inverse scattering problem in the polarization parameters domain for isotropic layered media solution via Newfon-Kantorovich iterative technique, 1994, J. Electromagn. Waves AppL, vol. 8, No. 6, pp. 759-779. 

Figure 5.19 Schematic representation of a thin-layer domain between flat surfaces...

Let H and L be two characteristic lengths associated with the channel height and the lateral dimensions of the flow domain, respectively. To obtain a uniformly valid approximation for the flow equations, in the limit of small channel thickness, the ratio of characteristic height to lateral dimensions is defined as e = (H/L) 0. Coordinate scale factors h, as well as dynamic variables are represented by a power series in e. It is expected that the scale factor h-, in the direction normal to the layer, is 0(e) while hi and /12, are 0(L). It is also anticipated that the leading terms in the expansion of h, are independent of the coordinate x. Similai ly, the physical velocity components, vi and V2, ai e 0(11), whei e U is a characteristic layer wise velocity, while V3, the component perpendicular to the layer, is 0(eU). Therefore we have... 

Fig. 3. An overview of atomistic mechanisms involved in electroceramic components and the corresponding uses (a) ferroelectric domains capacitors and piezoelectrics, PTC thermistors (b) electronic conduction NTC thermistor (c) insulators and substrates (d) surface conduction humidity sensors (e) ferrimagnetic domains ferrite hard and soft magnets, magnetic tape (f) metal—semiconductor transition critical temperature NTC thermistor (g) ionic conduction gas sensors and batteries and (h) grain boundary phenomena varistors, boundary layer capacitors, PTC thermistors.

Fig. 7. Thermomagnetic recording, (a) A focused laser beam generates a thermal profile in the magnetic layer, (b) The coercive force in the layer is reduced and its magnetisation can be reversed by a small magnetic field, here 30 kA/m. At room temperature, the coercive force is high and the written domains are...

From the write and read process sketched so far, some requirements for MO media can be derived (/) a high perpendicular, uniaxial magnetic anisotropy K in order to enable readout with the polar Kerr effect (2) a magnetoopticady active layer with a sufficient figure of merit R 0- where R is the reflectivity and the Kerr angle (T) a Curie temperature between 400 and 600 K, the lower limit to enable stable domains at room temperature and the upper limit because of the limited laser power for writing. 

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