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TUTORIALS FOR POWERBASE ======================= Powerbase is an extremely powerful program. Despite the fact that it is actually very easy to use its complexity and many features can make it difficult for the new user to get started. This booklet uses some ready made example databases supplied on the distribution disc to help familiarise you with the main functions of the program. It is made up of two sections. The first is a Quick Tutorial aimed at inexperienced users who may not have used a database before. The Main Tutorial is meant for people who, although new to Powerbase, have some familiarity with other databases. If you do fall into this category you should skip the Quick Tutorial and move straight on to the Main Tutorial. QUICK TUTORIAL ============== This tutorial is intended to acquaint the new user as painlessly as possible with the most commonly-used facilities of Powerbase. It does not explain how to create a database from scratch (see Chapter 4 − Creating a New Database − in the Manual), nor does it delve into the many advanced features, but it does explain how to:− (a) Start up Powerbase and open an existing database. (b) Browse through the database and search for individual records. (c) Add new records and alter or delete existing ones. (d) Query the database to create simple reports. (e) Close the database. The supplied sample database Friends is used to illustrate most of these activities. If you have a hard disc you should copy Friends and Powerbase itself onto it before proceeding further. It is possible to use Powerbase from floppy discs only but some operations, such as printing lists, will be quite slow. Unless memory is very tight users of floppy discs are recommended to allocate at least 32K to the RAM disc and copy Friends onto it. Everything will then run much faster. Powerbase can provide context-sensitive help via Acorn’s !Help application and you are advised to load this, resizing the help window and placing it at the top right of the screen. Further help can be had by choosing the Help entry which will be found on Powerbase’s main menu and also on the icon-bar menu. 1 Starting Powerbase ===================== Double-click on the Powerbase icon. After a few seconds it will appear on the icon-bar with the words “No data” beneath it to show that no database is open. Dragging the Friends icon onto the Powerbase icon on the icon-bar will open Friends for use and the words “No data” will be replaced by the name of the database. Two windows will open. One is the record window and displays the first record in the database, the one for Badgery Peter. The other is the keypad which allows you to control the browsing, searching and editing functions of Powerbase. The keypad is rather large and obscures quite a big area of the record window. The most-used buttons, however, are on the top two rows and clicking the “toggle size” icon (the small square at the right-hand end of the keypad’s title bar) will reduce the keypad to these two rows only. A second click restores it to full size. 2 Browsing and Searching ========================= Now that you have a database running we will find out how to move from record to record and how to access any specific record by using a small group of letters called the key of the record. All the mouse clicks referred to are made with the SELECT (left) button. If the chosen keypad action has an obvious opposite then you will find that using the ADJUST (right) mouse button brings about that effect. e.g. While SELECT on the top left keypad button takes you to the start of the file, ADJUST on the same keypad button takes you to the end. 2.1 Browsing through the Records -------------------------------- The top row of buttons on the keypad allows you to browse through the file. If you have !Help running, as previously suggested, it will tell you what each button does. Once you get the general idea you will find the symbols on the buttons logical and self-explanatory. The most commonly used ones act as follows:− (a) The arrows at the ends of the row take you to the first and last records. You are at the first record now, so click with SELECT on the top-right button and you will see the record for Turnip Charles. The leftmost button takes you back to the start again. (b) Movement through the file one record at a time is achieved using the single arrow keys next door to the ones you have just used. Try them out, noting the way records come up in alphabetical, or reverse alphabetical, order. (c) The keys with double arrows let you make longer jumps through a file. The number of records skipped is shown in the writable icon between them and has a default value of 10. As there are only 10 records in Friends these keys will have the same effect as the “first” and “last” keys, unless you make the interval smaller. Click in the icon, delete the 10 and enter 5 or 2, then try the double-arrow keys again. 2.2 Searching for a record -------------------------- The fifth button on the second row of the keypad shows a question mark followed by a “record card” icon. We will call it the Search button. When clicked with SELECT a small window opens on the right-hand side of the keypad. This is the Search window and contains a writable icon in which to enter the key of the record you wish to display. In this database keys are made up from the first 4 letters of the surname plus the initial so, if you wanted to call up the record for Bloggs Fred you would need to enter BLOGF. Do so then click on Find (or type the Return key on the keyboard) and the record will be displayed. Note that the key is shown in the window heading. If you enter the key of a non-existent record Powerbase displays the record which most nearly matches the key, but flashes the key field to warn you that what is being displayed is not what you asked for. 3 Editing the Database ======================= This part of the tutorial involves changes to the data. Make a working copy of the disc and put the original in a safe place. If you are using a copy of Friends on the RAM disc then the floppy disc won’t be altered, but it’s still not a good idea to work with the original disc. 3.1 Modifying records --------------------- Point the mouse at any field and click SELECT. The red text caret will appear in the field. The contents of the field may now be edited with the aid of the keystrokes which are standard for all RISC OS writable icons. i.e. Ctrl U clears the field. Delete removes the character to the left of the caret. Copy removes the character to the right of the caret. Shift/Copy deletes the word to the right of the caret. Ctrl/Copy deletes everything from the caret to the end of the line. ⇦ and ⇨ move the caret left/right by one character. Shift ⇦ and Shift ⇨ move the caret left/right by one word. Ctrl ⇦ and Ctrl ⇨ move the caret to start and end of the field. Having modified one or more fields you may be wondering what you have to do to make Powerbase save the modified record so that the changes won’t be lost. You don’t need to do anything! Powerbase will ensure that your changes are saved when you display a different record or close the database. 3.2 Recovering data after a mistake ----------------------------------- You may edit the wrong field by mistake and want to restore the previous contents. Call up Bloggs Fred’s record and change the address from “12 Woodland Road Exeter” to “12 Woodville Road Exmouth”. Now click MENU over the first line of the address. The second entry on the main menu (Field) contains a short group of letters called the tag of the field, in this case ADD1. Follow the right-pointing arrow to the Field sub-menu and choose the last entry; Undo changes. The contents of the field will revert to “12 Woodland Road”. Notice that only the first line of the address is affected; the town is still “Exmouth”. If you want to restore that field as well click MENU over it and follow the procedure just described. There might be occasions when you make a hopeless mess of a record and want to discard all the changes and revert to what you started with. You could, of course, “undo” each field separately as we just did for the street address and town but there’s a quicker way. Look near the bottom of the main menu, (just above Help) and you will see that here too is an Undo changes option. Choosing this undoes all the alterations you have made. It is important to realise that these facilities depend on the fact that Powerbase holds the currently-displayed record in memory and will therefore only work if the altered record has remained on display from the time you started changing it up to the point where you decided to “undo”. If you have looked at another record or clicked on Force update in the meantime then the changes will have been written to the disc and thus become “permanent”. 3.3 Adding and deleting records ------------------------------- To add a new record we use the Add record button which looks like a plus sign and an index card. Clicking on this offers a blank record into which you can type new data. You don’t have to complete all the fields, in fact the only field into which you must type something is the NAME field. This is the key field; the one from which the key, mentioned earlier, is derived. If you leave the key field blank then nothing will be written to the database. Type the name “Bodmin George”, then go to the beginning of the file and step through it record by record. You will find that your new record has been inserted in the correct place, i.e. the sequence goes: Badgery, Bloggs, Bodmin, Cavendish. Now try deleting the record you’ve just added. There is a “dustbin” button which will do exactly that, but don’t use it just yet. Make sure that the unwanted record is on the screen and click the button to the right of the dustbin. You will now find that Bodmin’s record has vanished; the names now run straight from Bloggs to Cavendish, just as they did before you added Bodmin. This looks a bit too easy. Suppose you clicked the keypad button by mistake and deleted an important record? No problem; what you have just done has been made easy because it’s far less drastic than it looks. The record hasn’t really been deleted at all. Click the button above the one you used for “deleting”. This shows a green right-pointing arrow and a card index icon. “Bodmin” will reappear. You will soon find, however, that it appears to be the only record in the file! Don’t worry; nothing has been lost. A Powerbase database is treated as six separate subfiles numbered 0−5. When you first open the database you are looking at Subfile 0 and the heading of the record window shows this. If you look at the heading now you will see that it has changed to Subfile 1. The buttons on either side of the bin carry pictures which suggest their true functions. They do not delete records; they merely move records from one subfile to another. The right button moves the displayed record to the next subfile in sequence. Thus, in the above case the “Bodmin” record has been moved from subfile 0 to subfile 1. A record in subfile 1 would be moved to subfile 2 and so on. When it gets to 5 the next click moves it into subfile 0 where it was originally. As you may have guessed, the left button moves records in the opposite direction, i.e. from subfile 1 to 0 or from subfile 0 to 5. If you do want to lose a record for good you consign it to the dustbin. As this button’s action is more drastic than that of the other two you are given a chance to change your mind. A window headed Powerbase: please confirm: will appear displaying the question Delete record permanently? Clicking OK causes the record to be deleted, Cancel removes the warning window from the screen leaving the record untouched. 4 Printing Lists ================= Before Powerbase can produce a list it must be told:− • which fields should appear on the list • which records should appear on the list 4.1 Making the field selection ------------------------------ Specifying the fields you want is extremely easy. To include a field point at it and click with ADJUST. The selected field will then appear with its foreground and background colours reversed. If you change your mind you can de-select it by clicking on it again with ADJUST. The order in which you select the fields is the order in which they will appear in the printed list. Take care with this as there is nothing on the screen to indicate what order the fields will be in. Field selections may be saved (using Save selection from the Print submenu) and reloaded for future use. For now select the name and the first 3 fields of the address. 4.2 Choosing which records to print ----------------------------------- Specifying which records to print is somewhat more complicated, although efforts have been made to render it as simple as possible. With the mouse pointer in the record window click MENU. This displays the main Powerbase menu from which you should choose Print. A small window appears in which you can specify the criteria which must be met by records for inclusion in the list. If you just click over the Print button (or type Return) without entering anything, you will obtain a list of the whole database (or, more accurately, of the the whole of the current subfile). Try this first. When the search is complete the list will be displayed in a window. If you point to a record in the list and double-click with SELECT Powerbase will display the chosen record in the main record window. Note that the caret is placed in the field you were pointing to on the list. This is very useful if you spot errors in the data whilst examining a list. A double click on the offending item offers the record with the caret correctly positioned for editing. Most queries involve printing only some of the records, not the whole database. To target a particular group of records we need to enter a search formula which will distinguish the records we want to print from all the rest of the records. Search formulae can be quite complex and a more detailed treatment is given in the Manual. Only a few simple examples are shown here. Enter the following and then click Print:− ADD2=Exeter The report window appears showing just one record: the one for “Bloggs Fred”. ADD2 is called the tag of the field. The label which appears beside a field on the screen is called its descriptor and you might have expected such labels to be used to refer to fields in search formulae. This is not done for two reasons:− (1) Descriptors can be inconveniently long for use in this way. (2) Fields don’t necessarily have descriptors. Of the 5 address fields only the first has a descriptor (Address). Since every data field needs a “handle” of some sort so that we can include it in search formulae we give each a tag, which is never more than 4 characters. Clicking MENU over a field makes its tag appear in the second menu item. The record for “Bloggs Fred” is, however, not the only one with an address in Exeter. There is another (“Sunningdale Samantha”) but with Exeter in ADDR3 rather than ADDR2. You can print both on the same list by using the formula:− ADD2,ADD3=Exeter Notice the way the alternative tags are separated by commas. We call this a tag list. A record will be printed if any one of the tags in the tag list is matched. The part of the search formula after the = sign is called the target and here too we may specify several in a target list. Try the following:− ADD3=Exeter,Anytown and also:− ADD2,ADD3=Exeter,Anytown The first of these examples prints the records for “Soap Joe” and “Sunningdale Samantha”, the second prints these two and “Bloggs Fred” as well. What the second formula is saying is “Print all the records which have either ‘Exeter’ or ‘Anytown’ in either the ADD2 or ADD3 field”. The characters we want to match don’t, of course, always make up the entire field. You can also search for part of a field. Suppose you wanted the records for people called Peter, Fred and Jean. Enter the formula:− NAME{Peter,Fred,Jean and you will find that the records for “Badgery Peter”, “Bloggs Fred” and “Ford Jean” are printed. The curly bracket (“{”) means “contains”. i.e. the name field doesn’t have to consist of Peter, or Fred or Jean, but has to contain one of these names somewhere within it. 4.3 Hard copy ------------- So far you have displayed reports in a window. If you want to send them to your printer run !Printers, switch on the printer, then click MENU over the displayed report. The Save as text option leads to a standard Save box from which you can drag the file icon to !Printers on the icon-bar. You could also drag it to a directory window to save it. Or you could simply type Return, in which case the report would be saved under a suitable default name in a directory called PrintJobs inside the Friends database directory. Every Powerbase database has a PrintJobs directory to use as a general dumping ground for reports and which needs to be cleared out periodically. 5 Closing down =============== A database may be closed down by choosing the Close database entry from the icon-bar menu. When you do so all relevant data stored in memory is saved to disc and the database is closed. You do not have to do anything to save the database file itself to disc since it has been there all along. Only the current record is in memory at any one time and this is automatically written back to disc when it has been changed in any way. If you are going to use another database straight away just double click on it or drag it to the Powerbase icon on the icon bar. In fact you don’t even need to close the previous database before doing this; Powerbase will do it for you. When working with a database on the RAM disc Powerbase will issue a warning that the data is not secure and that you need to drag it from the RAM disc to a floppy or hard disc before switching off. To terminate Powerbase itself use the Quit option on the icon bar menu. ============= MAIN TUTORIAL ============= This section is intended to acquaint a new user with the most commonly-used facilities of Powerbase. It does not explain how to create a database from scratch but it does explain how to:− (a) Start up Powerbase and open an existing database. (b) Browse through the database and search for individual records. (d) Add new records and alter or delete existing ones. (d) Query the database to create simple reports. (e) Close the database. The sample database Elements is used to illustrate these activities. If you have a hard disc copy Elements and Powerbase itself onto it before proceeding further. It is possible to use Powerbase with floppy discs but some operations, such as printing lists, will be slow. Unless memory is very tight users of floppy discs are recommended to allocate at least 112K to the RAM disc and copy Elements onto it, which will make it much faster. Powerbase can provide context-sensitive help via Acorn’s !Help application and you are advised to load this, resizing the help window and placing it at the top right of the screen. Further help can be had by choosing the Help entry on Powerbase’s main menu or on the icon-bar menu. 1 Starting Powerbase ===================== Double-click on the Powerbase icon. After a few seconds it will appear on the icon-bar with the words “No data” beneath it to show that no database is open. Dragging the ‘Elements’ icon onto the Powerbase icon on the icon-bar will open Elements for use and the words “No data” will be replaced by the name of the database. Double-clicking on the Elements icon has the same effect, in fact if Powerbase isn’t already on the icon-bar a double-click on Elements will install it for you provided that the Powerbase icon has been seen by the filer. Two windows will open. One is the record window and displays the first record in the database. The other is the keypad which allows you to control the browsing, searching and editing functions of Powerbase. The keypad is rather large and obscures quite a big area of the record window. The most-used buttons, however, are on the top two rows and the keypad can be moved part way off screen to get it out of the way. 2 Browsing and searching ========================= Now that you have a database running we will find out how to move from record to record and how to access any particular record by using a small group of letters called the key of the record. All the mouse clicks referred to are made with the SELECT (left) button. If the chosen keypad action has an obvious opposite then you will find that using the ADJUST (right) mouse button brings about that effect. e.g. While SELECT on the top left keypad button takes you to the start of the file, ADJUST on the same keypad button takes you to the end. 2.1 Browsing through the records -------------------------------- The top row of buttons on the keypad allows you to browse through the file. If you have !Help running, as previously suggested, it will tell you what each button does. Once you get the general idea you will find the symbols on the buttons logical and self-explanatory. The most commonly used ones act as follows:− (1) The buttons at the far left and right take you to the beginning and end of the file. The rightmost button takes you to ZIRCONIUM and the leftmost one to ACTINIUM. (2) Single arrows move by one record at a time. From ACTINIUM, clicking the right arrow takes you to ALUMINIUM. The left arrow takes you back to ACTINIUM. (3) Double arrows move through the file by longer jumps The right double arrow takes you from ACTINIUM to BISMUTH and the left one back to ACTINIUM. The “fast forward/rewind” value is shown in the box between these “fast wind” buttons. It is initially set to 10 but can be altered by clicking in it with SELECT and entering a new value. At either end of the file “wrap around” occurs. If you are at the last record (ZIRCONIUM) one record forward takes you to ACTINIUM again. Similarly, one record back from ACTINIUM goes to ZIRCONIUM. The second row has buttons marked like the “play” and “stop” controls of a cassette player. Play allows an automatic flip-through of the records without the need to touch any other buttons. When you get to the place you want, click on Stop. If the records go past too quickly you can slow the process down by increasing the number in the central icon of the top row of buttons. (This is normally used to set the “fast-wind” interval; see above.) 2.2 Key fields, Keys and Indices -------------------------------- When using the six buttons on the top row of the keypad you will have noticed that the records appear to be arranged alphabetically by the name of the element. The actual order in which records occur in the file is in fact nothing like alphabetical, but the order in which they are accessed is determined by an index which forces them to appear in alphabetical order. Every database must have at least one index, but you can have as many extra ones as you wish (subject to memory and disc limitations). The second row of the keypad has two buttons featuring a blue arrow with a key symbol. Click on the right one and the record for HYDROGEN is displayed! If you now experiment with the top row of buttons as before you will find that the records no longer appear in alphabetical order of name but in order of ATOMIC NUMBER instead. What we have done is change to a different index. If a database has several indices the “key” buttons allow you to cycle through them in opposite directions. (Since Elements has only two indices the two buttons have exactly the same effect.) When you change to a different index the screen always displays the first record as determined by that index. An index is built from keys which are derived from a particular key field. The two indices used by Elements are based on the NAME and ATOMIC NUMBER fields. The way in which the key stored in the index is derived from the key field differs in the two cases. For the NAME index the first four letters of the name are used. Since no two elements have names beginning with the same four letters this gives a unique value for the key. (Two letters would not be enough because of names like CHLORINE and CHROMIUM.) The ATOMIC NUMBER index is based on the whole 3-digit maximum length and the ordering is numeric. Whenever a record is displayed the key is shown in the window title (# characters are for padding and should be ignored.) The record screen shows which fields are key fields and which are not. The labels, or descriptors, of fields are normally black. Where the fields are key fields they are shown in dark blue instead and the field used by the current index has its descriptor in red. Note also that the background colour of the NAME field is pale yellow whereas the rest are white . This indicates that NAME is the primary key field. The primary key is more important than the others. The index based on it is the only one which a database must have and is the one selected when a database is first opened. 2.3 Searching for a record -------------------------- The fifth button on the second row of the keypad shows a question mark followed by a “record card” icon We will call it the Search button. When clicked with SELECT a small window, the Search window, opens to the right of the keypad. It contains a writable icon in which to enter the key of the record you wish to display. Suppose you want to see the record for the element NITROGEN. If the current index is the NAME then enter NITR and either type the Return key on the keyboard or click the Find button with SELECT. The required record quickly appears. If you enter the key of a non-existent record Powerbase displays the record which most nearly matches the key, but flashes the key field to warn you that what is being displayed is not what you asked for. You don’t necessarily need to type the whole key; NIT would do in this case, but NI would be ambiguous (there are elements called NICKEL and NIOBIUM). To find NITROGEN when the ATOMIC NUMBER index is active you would need to know that the atomic number of nitrogen is 7. Change key, enter this number and type Return or click on Find. The required record appears. Abbreviated keys are not allowed in this case for obvious reasons; if you want element 103 (LAWRENCIUM) it’s no good entering 10 (NEON)! You might want to examine a group of related records, e.g. the six similar elements LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM and FRANCIUM which are known as the Alkali Metals. You could, of course, look up each in turn by entering its key but there is a better way. Click on the Use filter button on the keypad. The button becomes ticked and the Filter window opens on the right of the keypad. This button is what we call an option switch and is used to turn a particular feature ON or OFF. The six elements referred to all occur in group 1 of the Periodic Table of the elements so type GP=1 into the writable icon. and click on Filter. The record for CAESIUM is displayed. If you experiment with the buttons on the top row of the keypad you will find that they behave as if the six Alkali Metals were the only elements in the database; all the rest have been “filtered out” so that you access only the ones you are interested in. To return to normal operation either click the Cancel button on the Filter window or turn off the switch on the keypad. 3 Editing the Database ======================= This part of the tutorial involves changes to the data records. Make a working copy of the disc and put the original in a safe place. If you are using a copy of Elements on the RAM disc the floppy disc won’t be altered, but it’s not a good idea to work with the original disc. 3.1 Modifying records --------------------- Pointing the mouse at any field and clicking SELECT places the caret in that field. The contents of the field may then be edited in the standard way for RISC OS writable icons. i.e. Ctrl U clears the field. Delete removes the character to the left of the caret. Copy removes the character to the right of the caret. Shift Copy deletes the word to the right of the caret. Ctrl Copy deletes everything from the caret to the end of the line. ⇦ and ⇨ move the caret left/right by one character. Shift ⇦ and Shift ⇨ move the caret left/right by one word. Ctrl ⇦ and Ctrl ⇨ move the caret to start and end of the field. Changes made to a record cause the record to be written back to the database whenever you display a different record or close the database. There is a button on the keypad called Force update but you don’t normally need to use it. 3.2 Using the scratchpad ------------------------ It is sometimes necessary to copy the contents of one field into another, either in the same record or a different record. This can be done with the aid of the scratchpad which is controlled by the two buttons at the ends of the third row on the keypad. Place the caret in the field you want to copy and click on the left button. This stores the contents of the field on the scratchpad. Moving the caret to another field and clicking the right button copies the data from the scratchpad into that field, over-writing its previous contents. You may continue to “paste” the data into new fields as often as you like. Only when you click the left button again are the contents of the scratchpad changed. Data pasted into a field will not be allowed to overflow; if too long for the field it will be cut to the permitted length. As an added precaution you can’t paste into a field if there is nothing on the scratchpad so accidental blanking of fields is avoided. 3.3 Undoing mistakes -------------------- You might edit the wrong field by mistake and want to restore the previous contents. Click MENU over the field. The second entry on the main menu contains the tag of the field. Follow the right-pointing arrow to the Field sub-menu and choose Undo changes. The previous contents of the field will be restored. Similarly, if you make a mess of a whole record and want to go back to the way it was you can choose Undo changes from the main menu. It is important to realise that the Undo facilities will not work if you have looked at another record before using them (or clicked on Force update). You can only recover data which has been altered in or removed from the currently-displayed record. 3.4 Adding new records ---------------------- First we will add a new record for a fictitious element as described below:− NAME TASMANIUM SYMBOL Ts ATOMIC NUMBER 108 The second button on the second row of the keypad has a plus sign and a “record card” icon. This is the Insert button. A blank record will be displayed with the caret in the NAME field. Enter TASMANIUM here and type Return. The caret will jump to the SYMBOL field. Enter Ts. You will now need to press Return twice to get to ATOMIC NUMBER (One press takes you to the un-named field after NAME where the origin of the element’s name is given.) Alternatively you could point the mouse at the ATOMIC NUMBER field and click SELECT. There is no need to press Return after entering a field in order to accept the data; it’s just the most convenient way of getting to the next field. When entering data into widely-scattered fields it is more convenient to use the mouse to move the caret. Having entered the data click any of the first row of buttons so a different record is shown. Now use Search to find TASMANIUM by name (its key will be TASM). Change to the other index and find it by atomic number. In both cases try moving to the record just before and just after the new one, noting that it has been placed in its correct position in both indices: between TANTALUM and TECHNETIUM in the NAME index and at the end of the ATOMIC NUMBER index. 3.5 Data Input Validation ------------------------- When entering the above data you may have noticed that the NAME field will only accept capital letters and the ATOMIC NUMBER field will only accept numerals. Any others are simply ignored. We call this feature character validation. Another level of data validation, which we will now illustrate, is called table validation Make an entry in the GROUP field. Type X, for example, then try to move to another field by either typing Return or clicking the mouse. You will find that you can’t do so; you get an error message instead. This is because the GROUP field is linked to a validation table which means that only entries which appear in the table may be used in that field. Fields linked to validation tables are distinguished by using dark green, instead of black, as the foreground colour. To see what the validation table contains, place the caret in the GROUP field then click on the List values button on the keypad. The validation table will be displayed in its own window. Only items in the left column of the table may be entered in the GROUP field. Element 108 would be a transition metal, so enter T. You will now find that Powerbase accepts your data. Both character validation and table validation may be turned off and on by means of a switch on the Preferences window. To get at this window click MENU over the Powerbase icon on the icon-bar and choose Preferences from the icon-bar menu. The rather large window which appears has a collection of option switches down its left-hand side. The sixth of these (Validate input) is normally ON to indicate that validation is in effect. Click to turn it off then click on Accept. The Preferences window will be removed from the screen and you will find that input is no longer being validated. 3.6 Deleting records -------------------- Since “tasmanium” isn’t a real element we want to remove it from our database. There is a “dustbin” button which will do exactly that but we won’t use it just yet. Make sure that the unwanted record is on the screen and click the button to the right of the bin. You will now find that TASMANIUM has vanished; the names run from TANTALUM to TECHNETIUM and the atomic numbers end with 103, just as they did before you added the extra record. What if you had clicked the button by mistake and deleted an important record? Powerbase handles this very nicely. The record hasn’t really been deleted at all. To prove this, click on the button above the one you used for “deleting”. This shows a green right-pointing arrow and a “card index” icon. TASMANIUM will reappear. You will also find that it appears to be the only record in the file! Don’t worry; nothing has been lost. A Powerbase database is treated as six separate subfiles numbered 0-5. When you first open the database you are looking at Subfile 0 and the heading of the record window shows this. If you look at the heading now you will see that it has changed to Subfile 1. The button you hav just clicked advances the subfile number by 1. Its counterpart on the left has the opposite effect. The buttons on either side of the bin carry pictures which suggest their true functions. They do not delete records; they merely move records from one subfile to another. The right button moves the displayed record to the next subfile in sequence. Thus, in the above case TASMANIUM has been moved from subfile 0 to subfile 1. A record in subfile 1 would be moved to subfile 2 and so on. When it gets to 5 the next click moves it into subfile 0 where it was originally. As you may have guessed, the left button moves records in the opposite direction, i.e. from subfile 1 to 0 or from subfile 0 to 5. If you do want to lose a record for good you consign it to the dustbin. As this button’s action is more drastic than that of the other two you are asked to confirm that this really is what you want to do before the deletion goes ahead. 4 Printing Lists ================= Before Powerbase can produce a list it must be told:− • which fields should appear on the list • which records should appear on the list. 4.1 Making the field selection ------------------------------ Specifying the fields you want is extremely easy. To include a field point the mouse at it and click with ADJUST. The selected field will appear with its foreground and background colours reversed. If you change your mind about a field you can de-select it by clicking on it again with ADJUST. The order in which the fields will appear in the printed list is the order in which you select them. Take care since there is nothing on the screen to indicate what order the fields will be in. The fields chosen for inclusion in a printout make up a selection which may be saved, using Save selection from the Print submenu, and reloaded for future use. Just for now select NAME, SYMBOL and GROUP. 4.3 Choosing which records to print ----------------------------------- Specifying which records to print is more complicated, although efforts have been made to render it as simple as possible. With the pointer in the record window click MENU. This displays the main Powerbase menu from which you should choose Print. A small window appears in which you specify the criteria which must be met by records for inclusion in the list. If you just click the Print button (or type Return) without entering anything here you will obtain a list of the whole database (or, more accurately, the the whole of the current subfile). Try this first. Nothing will be printed until the search is complete. If the mouse pointer is over the main window the hourglass will tell you how far things have progressed. Pressing Escape will cause the process to be aborted. When complete the list will be displayed in a window. Clicking MENU over it displays a menu which leads to a Save box. You may save the list as a text file by dragging the file icon to a filer window or print it by loading !Printers and dropping the file icon on the !Printers icon on the icon-bar. If you point to a record in the displayed list and double-click with SELECT Powerbase will display the chosen record in the main record window. Moreover the caret is placed in the field you were pointing to on the list. This is very useful if you spot errors in the data whilst examining a list. A double click on the offending item offers the record with the caret correctly positioned for editing. Most database queries don’t, of course, involve printing all the records. You will usually need to enter a search formula before clicking Print. You have already used a search formula when you typed GP=1 to “filter out” all but the six Alkali Metal records (see 2.3). Search formulae can be complex and a more detailed treatment is given in the Manual. Only a few simple examples are shown here. Suppose we want a list of all transitional elements. i.e. all those which have T in the GROUP field. We can do this by entering the search formula:− GP=T Why GP? GROUP=T seems the more obvious choice but Elements contains many fields which have no label, such as the one on the first line which gives the origin of the element’s name. Every field which can hold data has to have a handle by which we can refer to it and that handle is called the field tag. Tags are very short; never more than four characters. You have seen some tags already. Look at the list you printed earlier. The three columns are headed with the tags (NAME, SYM and GP) not the descriptors (NAME, SYMBOL and GROUP). We therefore meets tags in two contexts:− • specifying fields in search formulae • as the default column headings in lists The Print options window, displayed by choosing Options from the Print submenu, lets you change the column headings to field descriptors if you prefer them. Type GP=T in the space provided and click Print. This time the list will be a much shorter one and you will see that the GP column contains T in every case. The second example involves printing all elements whose names end in “IUM”. What we need to specify is that NAME contains IUM and we do this by entering the search formula:− NAME{IUM. Note the use of a left brace (curly bracket) to mean “contains”. Another way to perform this search is to use a wild-card. Type:− NAME=$IUM Clicking Print will produce the same list as before. The “$” is a wild-card character which can represent any number of unspecified characters. The search formula is saying in effect, “I don’t care what the first part of the name is as long as it ends with IUM”. We will combine the previous two examples into a two-pronged search for all the TRANSITIONAL elements whose names end in “IUM”. The search formula this time is either:− NAME{IUM AND GP=T or:− NAME=$IUM AND GP=T Note the spaces before and after AND. These are essential. You might like to try an alternative way of entering a search formula. Proceed as follows:− 1. Click the Help button on Print window. This opens the Help window. 2. NAME should already be visible as the required field, but you need to select the radio button for contains. 3. Click in the space next to Value and enter IUM. 4. Click Add to formula. The search formula now reads NAME{IUM. 5. Click the AND button. 6. Click on the “menu” button to the right of the tag display and choose item 6 (GP) 7. Select the radio button for is equal to 8. Enter T in the Value field. 9. Click Add to formula The complete search formula should now be visible so click Print and the list will be produced. The procedure takes far longer to describe than to do and can be a great help to the infrequent Powerbase user who has trouble remembering the syntax of search formulae. If you use complex queries often you may find it convenient to save them for future use. Save query from the Print submenu enables you to do this. The biggest problem you are likely to encounter is not knowing the tags for the various fields. By using the above method you can see all the tags displayed in a menu or cycle through them using a pair of arrowheads called “bump” icons. It is also useful to know that clicking with SELECT on a field while holding down Ctrl causes the tag of that field to appear in the search formula icon. 5 Merging data into an Impression document =========================================== The distribution disc contains a simple Impression document called MergeTest. It will be used in conjunction with the Elements database to illustrate direct data-merging with Impression. (1) Ensure that Impression has been “seen” by the filer. (You need not actually load it.) (2) Open the Elements database and drop MergeTest onto the record window. The Data merge window will appear. (3) Click on Merge. You will see that data relating to the record for ACTINIUM has been inserted into the Impression document. (4) The arrow and double-arrow buttons, identical to those on the keypad, may be used to move through the database merging different records into the document. (5) A search formula may be used to restrict the operation to records matching certain criteria. (6) Print may be used to print the document with the currently-merged data. To print a set of documents, one for each matching element, select Print all then click on Merge. During data-merging Impression editing is disabled; you can’t place the caret in the document and the mouse pointer appears as a red and blue cross. Clicking on Cancel or closing the Data merge window restores normal editing. For more information on data-merging, including instructions on how to prepare the Impression document, see Ch 9 in the Manual. 6 Closing down =============== A database may be closed down by choosing the Close database entry from the icon bar menu. When you do so, all the indices stored in memory are saved to disc and the database is closed. You do not have to do anything to save the database itself to disc since it has been there all along. Only the current record is in memory at any one time and this is automatically written back to disc when it has been changed in any way. Also saved automatically is the link file which holds the relational links between the main database and the validation tables. The tables themselves are also saved. There’s also an Abandon database entry on the icon-bar menu. This too will close your database but without saving new data to the disc. It is really intended as the quickest way to close a database which you have opened simply for examination. If you are entering data for real you should use Close database. If you are going to use another database straight away just double click on it or drag it to the Powerbase icon on the icon bar. In fact you don’t even need to close the previous database before doing this; Powerbase will do it for you. When working with a database on the RAM disc Powerbase will issue a warning that the data is not secure and that you need to drag it from the RAM disc to a floppy or hard disc before switching off. To terminate Powerbase itself use the Quit option on the icon bar menu.