Overview of LocalTalk Protocol

LocalTalk refers to the physical networking -- that means the built-in controller in many Apple computers, the cables and the expansion cards required on some systems. The "official" Apple cabling system typically uses a "bus topology" where each device in the network is directly connected to the next device in a daisy chain. The illustration on the Farallon book cover below gives an idea of how a bus looks.
Ethernet is the most-used method of Macintosh networking and all new Macs sport an Ethernet port, but the longevity of Macs mean there's still a bunch out there with serial ports (i.e., LocalTalk support) but no Ethernet. New iMacs and G4s lack serial ports, so can't network directly with older LocalTalk Macs and printers.

LocalTalk implementation utilized the Mac's RS-422 printer port with twisted-pair cabling and 3-pin DIN connectors. Systems were daisy-chained together and required adapters to work with the Mac's onboard DB-9 or 8-pin DIN connectors. LocalTalk provided a fairly speedy 230.4 kbps networking speed, very useable for file sizes and traffic levels of the day - compare this to the still used 56 kbps modem.

A variation of LocalTalk, called PhoneNet used standard unshielded twisted pair telephone wire with 6 position modular connectors (same as used in the popular RJ11 telephone connectors) connected to a PhoneNet transceiver, instead of the expensive shielded twisted-pair cable. In addition to being lower cost, PhoneNet-wired networks were more reliable due to the connections being more difficult to accidentally disconnect.
A LocalTalk-to-Ethernet Bridge is a network bridge that joins the physical layer of the AppleTalk networking used by previous generations of Apple Computer products to an Ethernet network. Some LocalTalk-to-Ethernet Bridges only performed Appletalk bridging. Others were also able to bridge other protocols. For example: TCP/IP in the form of MacIP.

Conceptual Data Models for Database Design

Conceptual modeling is an important phase in designing a successful database application. The database design process consists of a number of steps listed below:

Step 1: Requirements Collection and Analysis
- Prospective users are interviewed to understand and document data requirements
This step results in a concise set of user requirements, which should be detailed and complete.
- The functional requirements should be specified, as well as the data requirements. Functional requirements consist of user operations that will be applied to the database, including retrievals and updates.
- Functional requirements can be documented using diagrams such as sequence diagrams, data flow diagrams, scenarios, etc.



Step 2: Conceptual Design / Data Modeling
- Once the requirements are collected and analyzed, the designers go about creating the conceptual schema.
- Conceptual schema: concise description of data requirements of the users, and includes a detailed description of the entity types, relationships and constraints.
- The concepts do not include implementation details; therefore the end users easily understand them, and they can be used as a communication tool.
- The conceptual schema is used to ensure all user requirements are met, and they do not conflict.

Step 3: Database Design
- Two sub-steps called Database Logical Design which define a database in a data model of a specific DBMS and Database Physical Design which define the internal database storage structure are defined.
- It also defines file organization or indexing techniques.

Step 4: Database Implementation
- Many DBMS systems use an implementation data model, so the conceptual schema is transformed from the high-level data model into the implementation data model.
- This step is called logical design or data model mapping, which results in the implementation data model of the DBMS.

Step 5: Physical Design
- Internal storage structures, indexes, access paths and file organizations are specified.
- Application programs are designed and implemented.