Holos

Holos is an influential OLAP (Online Analytical Processing) product of the 1990s. Developed by Holistic Systems in 1987, the product remained in use until around 2004.

Conception

The Holos product succeeded an older generation of mainframe products such as System-W. It was the first to use an industry standard SQL database (as opposed to a proprietary one), and also the first to use the new GUI PC for the user interface. In physically separating the "number crunching" from the user interface, the product was immediately client/server, although the term didn't come into use until some time later. The client/server model used for Holos was known as a 'processing server'. In addition to data services, the Holos Server supplied business logic and calculation services. It also provided complementary services to the Holos Client which meant the internal processing associated with the report writer, worksheet, etc., was distributed between the two components.

Architecture

The core of the Holos Server was a Business Intelligence (BI) virtual machine. The Holos Language (HL) was compiled into a soft instruction code, and executed in this virtual machine (similar in concept to Java in more modern systems). The virtual machine was fully fault-tolerant, using structured exception handling internally, and provided a debugger interface. The debugger was machine-level until quite late on, after which it also supported source-level access.

The virtual machine accounts for one of the most misunderstood aspects of the product: OLAP data was handled as a core data type of HL, with specific syntax to accommodate multidimensional data concepts, and complete programmatic freedom to explore and utilise the data. This made it very different from the industry trend of query-based OLAP and SQL engines. On the upside, it allowed amazing flexibility in the applications to which it could be applied. On the downside, it mean that 3-tier configurations were never successfully implemented since the processing had to be close to the data itself. This hindered large-scale deployment to many clients, and the use of OLAP data from other vendors. In reality, its own data access times were probably some of the fastest around -- at the individual cell level; they had to be in order to be practical. However, when fetching back bulk data for non-cooperating clients, or data from other vendors, the queries could not be optimised as a whole. Its own data access used a machine-wide shared memory cache.

Language

The Holos Language was a very broad language in that it covered a wide range of statements and concepts, including the reporting system, business rules, OLAP data, SQL data (using the Embedded SQL syntax within the hosting HL), device properties, analysis, forecasting, and data mining. It even supported elements to enable self-documentation and self-verification. Placing all these areas on a common footing, and allowing them to co-operate by sharing data, events, etc., was key to the number of possibilities that resulted. For instance, the report writer supported input as well as output, plus interactive graphics, and a comprehensive event mechanism to pass back information about the viewed data to event handlers. Also, reports and data were separate entities, thus allowing the same report to be applied to different data as long as it was described by similar meta-data. This meant that when terms like EIS and MIS were first coined, the industry norm was "slideshows", i.e. pre-programmed transitions between views, whereas Holos provided data-driven drill-down, i.e. no pre-programmed views or links. The transitions could be made dependent upon the data values and trends, in conjunction with the available business logic.

OLAP Storage

Holos Server provided an array of different, but compatible, storage mechanisms for its multi-cube architecture: memory, disk, SQL. It was therefore the first product to provide "hybrid OLAP" (HOLAP). It provided a very versatile mechanism for joining cubes, irrespective of their storage technology, dimensionality, or meta-data, and this was eventually given a US patent (called COA -- Compound OLAP Architecture US patent|6289352US patent|6490593). One novel aspect of this was a 'stack' feature that allowed read/write cubes to be stacked over read-only cubes. Read operations to the overall virtual cube then visited both 'racks' (top first, and then the bottom), whereas write operations only affected the top. The resulting valve-like mechanism found many applications in data sharing, what-if forecasting, and aggregation of slow SQL-based data. Since the overhead of the joining was small, it was not uncommon to have stacks 7 levels deep, and joining terabytes of real OLAP data. Around about V8.5, Holos Server implemented a hierarchical lock manager, allowing nesting of fine and coarse-grain OLAP locks, and full transaction control.

Business Rules

The business logic supported full cross-dimensional calculations, automatic ordering of rules using static data-flow analysis, and the identification and solution of simultaneous equations. The rules treated all dimensions in an orthogonal fashion. The aggregation process did not distinguish between simple summation or average calculations, and more complex non-commutative calculations. Both could be applied to any dimension member. The process allowed aggregation levels (i.e. those calculation levels starting with base data (level 0) and proceeding up to the overall grand total) to be individually pre-stored or left to be calculated on demand.

Holos Client

The Holos Client was both a design and delivery vehicle, and this made it quite large. Around about 2000, the Holos Language was made object-orientated (HL++) with a view to allowing the replacement of the Holos Client with a custom Java or VB product. However, the company were never sold on this, and so the project was abandoned.

One of the biggest failures was not to provide a thin-client interface to the Holos Server, and this must have contributed to the product's demise. Although an HTML toolkit was sold, it was clumsy and restricted. By the time a real thin-client mechanism was developed, it was far too late and it never got to market.

Deployment

Before its demise, the Holos Server product ran under Windows NT (Intel and Alpha), VMS (VAX and Alpha), plus about 10 flavours of UNIX, and accessed over half-a-dozen different SQL databases. It was also ported to several different locales, including Japanese.

Company

Holistic Systems was purchased by the hardware company Seagate Technology in 1996. Along with other companies such as Crystal Services, it was used to create a new subsidiary company called Seagate Software. After some manipulation and selling off, only Holistic and Crystal remained, although, like a game of chess, positions of power and control were sought by those who stayed. Most of these fell to Crystal, and eventually the company was renamed Crystal Decisions. After some in-fighting and argument over product strategy, the main Holos development team finally started to leave around 2000, and Crystal Decisions was finally taken over by Business Objects in 2004. Following the takeover, support for Holos was outsourced to Raspberry Software, which was set up by former employees of Crystal Decisions.