Chapter 4 - Software System Layers and Pillars

From the SoProTech perspective, a generic software system can be structured according to three abstract layers (often referred to as tiers) and two cross-layer pillars, as shown by the next figure. Layers and pillars are collectively referred to as software system logical blocks.

Figure 3 - Software system layers and pillars

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The following paragraphs describe the relationship between software layers and pillars on one hand, and Software Entities on the other. As explained in more detail in the next chapter , each Software Entity file is divided in sections, roughly corresponding to the logical blocks illustrated above. In a similar way, Software Molds in a Somusar/Software Mold Kit[tm] are divided in five groups, one for each software system layer and pillar, as explained in chapter 6 .

4.1 - Core Features        top

The core features of a Software Entity in a software system are defined, in the SoProTech context, as the identification block for the entity and the complete set of data fields, data processing functions, and relationships with other entities, that concur to characterize that entity across all layers of the software system. In other words, the core features of an entity consist of the complete collection of the components of all the layer-specific entity facets.

Within a Software Entity file, the core features of an entity are described in sections CORE and DEFS, which stands for definitions.

4.2 - Data Base Storage        top

In many cases the most straightforward implementation of the data base layer, or data storage layer, consists of a relational SQL data base. In addition to RDBMS the DB layer may also include other software mechanisms that ensure the so-called persistence of the data of an entity: hierarchical databases, transactional systems, plain file systems, custom data management legacy procedures, or even the back-ends of complex ERP (Enterprise Resource Planning) or CRM (Customer Relationship Management) packages, all these data management systems logically correspond to this layer.

The data storage facet, or facets, of an entity can be defined in section DB of the corresponding Software Entity file.

4.3 - Logic        top

The business logic, or data processing layer of a software system is the junction layer between the data base and the usage interface layers: the data flowing back and forth between the DB and UI layers are processed by classes, or procedures, implemented by means of programming languages in a strict sense, ranging from older languages such as COBOL, RPG and C, to newer languages such as Java[tm], C++, C#. Scripting languages like Perl are also often used in this layer.

The LOGIC section of a Software Entity file is the repository for the entity facet (or facets) on the logic layer.

4.4 - Usage Interfaces        top

The third layer of a typical software system is the usage interface layer, or data presentation layer. The SoProTech particularly emphasizes the fact that an entity usage interface design should cover not only the (human) user interface - usually a GUI -, but it should also comprise generic usage interfaces for other systems, such as protocol packet or data exchange representations, that can be implemented as a Java[tm] class or a C struct, or as an XML document, along with other source code.

In most cases, however, the corresponding section UI in a Software Entity file will probably contain one or more human-oriented views of the entity data fields and processing functions. The SoProMach will in this case translate those views into generated files in one or more GUI-oriented languages, such as HTML, XML, Visual Basic®, or JSP[tm] (JavaServer Pages[tm]).

4.5 - Documentation        top

An additional pillar of software is represented by the system documentation, called DOC in SoProTech terminology, that should describe the implementation of the software in a more or less technical language, depending on the type of reader that the documentation is intended for. The SoProTech allows documentation to be generated at the same time that the software is generated, thus ensuring a high degree of consistency between the software and the documentation, which is thus always up-to-date.

The generation of documentation follows exactly the same scheme as for the generation of software for the layers previously discussed.

Logical block DOC has one peculiarity with respect to layers DB, LOGIC and UI: Software Entity files do not have a DOC section, as the files produced by the SoProMach should document the role and function played by the entity across the layers of the software system, and those role and function are already described in the other sections of the entity file.

4.6 - Adjusting        top

In real world projects it is often necessary, and even advisable, to make use of tools equipped with a flexible tolerance mechanism, so that automatic production processes provide some room for manual corrections and adjustments, that can be then automatically applied by the same tools. For this purpose Software Entity files contain an ADJUST section, that allows entity designers to define and tune localized parameters for any given entity, thus influencing the software generation phase of SoProTech.

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