AM1 - 2. lecture

To build a the whole system for a company, many layers and systems are used.

to abstract from software, hardware, functions, processes etc.
in a company we have domains (sales, HR, finance, production…)
- each domain uses a application (CRM = customer relationship management, OMS = order management system etc.)
- different abstract applications and systems that make up the whole enterpise system in the company
  - all these systems require software, hardware and be connected to other systems
- each application is used by different roles within the company (or customers) and their needs have to be satisfied
different roles for architects
- Enterprise architect
  - manages the whole enterprise system and their connection
- Solution architect
  - manages the specific domain to satisfy the business needs
- Technical architect
  - manages the specific technical part (API, Cloud, Security etc.)

centralised - with a central server and their clients
- SPoF = single point of failure
- mostly the solution for enterprise systems
  - enhanced with P2P principles (such as messaging systems)
P2P (decentralized) systems = peer to peer systems
- decentralized, if one node fails, other nodes can take up it’s function
- highly scalable
- use of messaging systems in enterprise systems

when all applications are connected together (one action depend on another, one affects data and another act by it etc.), many integration issues can arise - they are solved by:
- standard interfaces (or mediators/adapters)
- message exchange formats, common and understandable data representation
- standardization of semantics of the data (this is often difficult)
- orchestrating of processes and functions

the system needs to be separated into layers, which should not overlap
- Návrh architektury aplikace
  - separation to presentation, application, data
  - thick client = presentation + application
    - - database on a server (data layer)
  - thin client = presentation
    - - app server + database server
  - multi-tier client/server
    - additional layers of middleware (value added to the communication)
      - could be individual layer of e.g. Enterprise service bus
  - thin client + microservices Microservices
    - there has to be a service orchestration layer (Kubernetes, clusters)
- GRASP - Nízká provázanost = loose coupling
layer communicate through interface
- Části interface
  - = “Agreement (contract) between two or more layers during communication”
  - defines: data formats, functions available, process interface (state transitions), technical interface (HTTPS, ports, authentications)

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