SaaS (Software as a Service)

How SaaS (Software as a Service) works

With SaaS, the application runs entirely in the provider’s data center. The customer receives login credentials and works through the browser or a lightweight app – with no installation routine, no database of their own and no responsibility for operating-system patches. The software is "rented" as a service rather than acquired as a product.

The core principle behind this is multi-tenancy: a single software instance serves many customers (tenants) at the same time. Each tenant sees only its own data and settings, but technically they all share the same code and the same infrastructure. That significantly lowers the cost per customer and lets the provider roll out improvements to everyone at once.

SaaS is billed by usage rather than by ownership. A subscription per user and month is common, often tiered into plans with different feature scopes. Additional users, storage, tenants or modules can usually be added and removed at any time. This usage-based licensing logic makes costs predictable and turns large one-off investments into ongoing operating expenses.

SaaS, PaaS and IaaS: the three cloud layers

SaaS is only one of three common cloud service models, which differ in how much responsibility lies with the provider and how much with the customer. A simple analogy: IaaS supplies the building blocks, PaaS the workshop, SaaS the finished tool.

SaaS vs. on-premise: the central contrast

The counter-model to SaaS is on-premise: here the customer buys a license and installs the software on their own or rented servers, which they operate themselves. They retain full control over data, infrastructure and the timing of updates – but also bear full responsibility for hardware, security, backups and updates, along with higher upfront investment.

SaaS shifts this burden to the provider and swaps one-off investments (CapEx) for ongoing operating costs (OpEx). The choice between the two models is one of the fundamental decisions in ERP selection and depends on requirements around data sovereignty, depth of customization, IT resources and budget structure. Some systems are deliberately offered in both variants.

SaaS in the ERP context

In the ERP field, SaaS has become the standard model for new implementations, especially in the mid-market and e-commerce. A cloud ERP delivered as SaaS bundles inventory management, order processing, purchasing and often accounting into one centrally operated application that is reachable from anywhere and continuously improved. Integrations to shops, marketplaces and shipping providers typically run through an API.

For growing merchants, the scalability is appealing: users, tenants or channels can usually be added without procuring new hardware. At the same time, SaaS in the ERP space demands a clear view of ongoing costs (TCO), data sovereignty and the question of how easily you can switch providers again later.

A SaaS ERP must meet the same legal requirements as an installed solution – for example the audit-proof, tamper-resistant retention of accounting-relevant documents. The fact that the software runs at the provider does not release the company from its responsibility for proper processes; it should clarify in advance how the provider technically handles traceability, data export and retention periods.

Benefits and limits of SaaS

The strengths of SaaS lie in rapid availability, low operating effort, predictable costs and always up-to-date software. Small and mid-sized companies without their own IT department gain access to applications they would be overwhelmed to run themselves. New features and security patches arrive automatically.

Limits show up around data sovereignty and dependency: the data resides with the provider, whose location, security level and continued existence become relevant. Customization is often only possible within the intended scope, and the tight bond to one provider can lead to vendor lock-in that makes a later switch harder. On top of that comes dependence on a stable internet connection and the provider’s availability: if their service goes down, work grinds to a halt – a reason to scrutinize the availability levels (SLA) and response times guaranteed in the contract. Ongoing subscription costs can also add up to more than a one-off purchase over the years. Anyone adopting SaaS should examine data protection, an exit strategy and contract terms early on.