Software architecture#

What is software architecture?#

Software architecture refers to the fundamental structures of a software system and the discipline of creating such structures and systems. Each structure comprises software elements, relations and properties of both elements and relations.

Software architecture is usually represented with a model.

Architecture model#

Architecture modeling have the following characteristics:

• It represents a set of structures necessary to reason about a system.
• It is an abstraction that dispenses with details.

Architectural points of view#

Architecture can be defined from physical or logical point of view.

Physical architecture#

Physical elements for software execution:

• Hardware
• Third party software
• Other elements external to the application

Logical architecture#

Software components. Group the different functionalities.

• It deals with the public part of the elements of the system.
• Describes the software components, the relationships between them and their properties
• Ignores the internal implementation of the components

Mixed architecture#

It is also usual to represents both together: physical as tiers, logical as layers.

Architecture layers#

Each architecture layer, has a specific purpose.

Presentation layer#

• Displays the user interface
• Facilitates user interaction with the system
• Server-side contains a component that generates and serves the HTML.
• Client-side contains a browser that displays HTML and executes scripts.
• Computational load:
  • Traditionally the presentation logic was server-side.
  • Technologies such as AJAX allow logic to be executed on the client-side.

Business layer#

• Includes business logic
• Allows reuse of business logic functions
• Enables improved maintenance and testing

Data layer#

Abstracts the logic needed to access the DB.

Service layer#

• Encapsulates access to external services residing on a remote machine
• The system itself can be offered as web services.

Architecture scalability#

Scalability is how increased data usage and growth affects performance.

It is important:

• The correct dimensioning of the application
• The adaptability of the system to increased demand.

There are two ways of scaling a system: vertical or horizontal scaling.

Vertical scaling#

Adding more power to the machine hosting the system

• Faster CPU
• More RAM
• SSD disks

Horizontal scaling#

Creating system clones and load balancing. Balancing can be done by hardware or software.

Hardware balancing#

Different requests from the same user can be handled by different clones.

Based on routing, tunneling or IP translation.

Software balancing#

All requests from a user are served by the same clone.

Done by inspecting HTTP packets to maintain the user session in the same machine.

Architecture patterns#

They describe a general solution to a design problem that is frequently encountered.

• Are general organization schemes of a system
• Specify a series of subsystems or components and their responsibilities
• Define rules for organizing the interactions between them

More about architecture patterns here.

Architectural modeling in UML#

Components diagram#

A component diagram is composed of software components.

A software component is a composition unit with all its interfaces and context dependencies explicitly defined.

Components properties#

• Ports: Connection points between your internal structure and your environment.
• Interfaces: Services offered and required to compose it with others.
• Realizations: The classes that implement it.
• Artifacts: The physical files that enable its deployment.
  • Source files
  • Scripts
  • Executables

Deployment diagram#

Shows the communication topology of a distributed system.

• They represent the nodes or devices of the system
• The connections between the nodes
• The assignment of artifacts and software components to each node

It is the highest level diagram in UML.

The use of visual stereotypes allows a particularized representation of the deployment diagram.