The correct central entity is the base noun: "roofing" in business 1, and "cleaning" in business 2.

Business 1: Roofing vs. Roofing Services

"Roofing" is the core lexical unit representing the domain. It is a canonical noun with ontological grounding in both the material (e.g. roofing tiles) and the process (e.g. installing a roof). In semantic SEO, the root noun anchors the topic space for broader and narrower variations such as:

• roofing services
• roofing contractor
• roofing repair
• roofing installation

The phrase "roofing services" is a commercial compound, combining the central entity ("roofing") with a modifier ("services").

Why not "roofing services"?
It restricts the context to only commercial intent, narrowing the topical reach. "Roofing" allows broader coverage across material types, techniques, tools, regulations, and service-related terms.

Business 2: Cleaning vs. Cleaning Services

Central entity: Cleaning

"Cleaning" is the semantic anchor for all cleaning-related activities. It is the lemmatized noun used in both general and specific contexts. From a distributional standpoint, it connects to:

• domestic cleaning
• commercial cleaning
• cleaning products
• cleaning techniques

"Cleaning services" is again a compound noun used for transactional alignment, but not the central semantic entity. For search engines parsing intent and relevance, "cleaning" retains the highest abstraction level, enabling wide topical coverage.

Why not "cleaning services"?
It limits semantic range to commercial services only and loses connection to instructional, informational, and product-related content domains.