N-tier architecture
Spreading an application across several machines: one, two, three tiers and more, thin or thick client, and the difference between a tier (physical) and a layer (logical).
- 21 cards
- 5 topics
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A few cards from the deck
Tier: what is it?
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A level of an application deployed on its own machine or process: screen, processing or data.
A tier is deployed, scaled and protected separately. A layer, on the other hand, is a logical split of the code that may sit within a single tier.
A desktop application has three code layers (presentation, business, data access) and keeps its data in an SQLite file it opens itself: everything runs in a single process on the workstation. How many tiers does it have?
- One, because everything runs in the same place
- Three, because each code layer forms a tier
- Two, because the database forms a separate tier
- None, because tiers only concern the web
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One, because everything runs in the same place
A tier is a unit of deployment, not a bundle of classes. SQLite is a library loaded into the process, not a separate server: three logical layers in the same process make just one tier.
A classic web application has three tiers: the browser is the … tier, the application server the … tier, and the database the … tier.
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A classic web application has three tiers: the browser is the presentation tier, the application server the processing tier, and the database the data tier.
Each tier runs on its own machine or process, and only the middle tier is allowed to reach the data tier.
Client-server architecture: what is it?
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An organisation in which a requesting program, the client, sends requests to a providing program, the server, which handles them and answers; its basic form has two tiers.
In its simplest form, the thick client holds the business rules and the server is just a database: every rule change forces a redeployment to all workstations.